On the morning of September 11, 2001, millions of Americans watched in disbelief as two commercial airplanes, hijacked by members of the al-Qaeda terrorist network, struck the twin towers of the World Trade Center in New York City. A third plane hit the Pentagon outside Washington, D.C. A fourth, United Airlines Flight 93, crashed in a field in Shanksville, Pennsylvania, after passengers struggled with the hijackers to prevent another strike on a national landmark. Nearly three thousand people died. They were office workers, firefighters, police officers, restaurant employees, flight attendants, passengers, and first responders. They came from more than ninety countries. In minutes, the United States had experienced the deadliest terrorist attack in its history, and the nation would not be the same again.

The attacks of September 11, 2001, opened a new era in American life. The federal government launched two wars — in Afghanistan and Iraq — that would last for decades. Congress passed sweeping new surveillance and law enforcement powers through the USA PATRIOT Act. A new federal agency, the Department of Homeland Security, reorganized the government's approach to domestic security. The country entered a prolonged debate about security versus civil liberties. The wars overseas would claim thousands of American lives and hundreds of thousands of lives in Afghanistan, Iraq, and across the Middle East.

Yet the twenty-first century was not only defined by terrorism and war. It was shaped by economic catastrophe: the Great Recession of 2008–2009, the worst financial collapse since the Great Depression, wiped out trillions of dollars in household wealth, cost millions of Americans their homes, and reshaped the economy for years. The recession accelerated economic inequality that had been growing for decades, creating a United States in which the very wealthy captured an ever-larger share of national income while working families struggled with stagnant wages, rising costs, and uncertain employment.

The twenty-first century also brought a transformation in American politics. Barack Obama's election in 2008 as the first African American president marked a historic moment. His presidency generated both hope and fierce opposition. After Obama, Donald Trump's election in 2016 broke with nearly every political norm, reshaping the Republican Party around economic nationalism, hostility to immigration, and attacks on democratic institutions. Trump's presidency culminated in the January 6, 2021, assault on the United States Capitol — an event with few parallels in American history. Joe Biden's election in 2020 restored a more conventional presidency but did not resolve the deep polarization dividing the country.

Running through all of these developments was an accelerating transformation in communications technology. Social media platforms changed how Americans received information, formed communities, and engaged in politics. The collapse of local newspapers and the rise of algorithmic content delivery created an environment in which misinformation spread rapidly. Democracy required a shared factual foundation; social media made that foundation harder to maintain.

Rights and social movements shaped the period as powerfully as political leadership. Movements for racial justice, LGBTQ equality, women's rights, immigrant rights, disability rights, and Indigenous sovereignty all gained strength in the twenty-first century, producing legislative victories, cultural changes, and fierce political resistance. Climate change emerged as perhaps the defining long-term challenge of the century, while the COVID-19 pandemic of 2020–2022 exposed the vulnerabilities of the public health system and the consequences of political division in the face of a shared health crisis.

This chapter examines the twenty-first century as a period of transformation, crisis, and contest. It follows the events and trends that define contemporary America not to deliver a verdict on the era but to help students understand how the long arcs of U.S. history — inequality and democracy, expansion and rights, nativism and pluralism, war and reform — continued to shape the nation into the present.

To understand the twenty-first century, students must understand the decades that shaped it. The United States that entered 2001 was the world's dominant military and economic power. The Cold War had ended a decade earlier with the collapse of the Soviet Union. The 1990s had brought relative prosperity, a technology boom, a budget surplus, and a sense among many Americans that history had settled into a stable liberal order. Yet beneath the surface, deep forces were building that would define the new century.

Economic inequality had been rising since the 1970s. The shift from a manufacturing economy to a service and finance economy, the decline of unions, the policy choices of the Reagan and post-Reagan eras, globalization, and technological change had all widened the gap between wealthy Americans and working-class Americans. By 2000, the United States had higher levels of income inequality than any other wealthy democracy. The gains of economic growth flowed disproportionately to those at the top.

The political system had become increasingly polarized. The ideological sorting of the two parties — with conservatives moving into the Republican Party and liberals into the Democratic Party — had accelerated since the 1960s and 1970s. The bitter partisan battles of the 1990s, including the Republican-led impeachment of President Bill Clinton in 1998, signaled that partisan conflict would intensify. The disputed presidential election of 2000, in which the Supreme Court halted the Florida recount and handed the presidency to Republican George W. Bush over Democrat Al Gore, deepened the sense of a politically divided nation.

Internationally, the United States faced a world of rising complexity. Al-Qaeda, a Sunni Islamist terrorist network founded by Osama bin Laden, had declared war on the United States and carried out attacks against U.S. targets through the 1990s, including the 1998 bombings of American embassies in Kenya and Tanzania and the 2000 bombing of the USS Cole. The environmental and scientific communities had been issuing increasingly urgent warnings about climate change since the 1980s. Into this world came the September 11 attacks, which transformed American politics, foreign policy, domestic security, civil liberties, and international relations for decades.

The morning of September 11, 2001, began with clear skies over the eastern United States. By mid-morning, it had become the most catastrophic day on American soil since the Civil War. Nineteen hijackers affiliated with the al-Qaeda terrorist network took control of four commercial airplanes. Two planes struck the North and South Towers of the World Trade Center in lower Manhattan, causing both towers to collapse. A third plane struck the western face of the Pentagon, killing 184 people. United Airlines Flight 93 crashed in Shanksville, Pennsylvania, after passengers attempted to retake the aircraft. In total, 2,977 people were killed — coming from more than ninety countries.

The attacks were spectacular in their ambition and devastating in their execution. Television networks broadcast the events live, meaning millions of Americans watched in real time as the towers burned and fell. For a generation of Americans, September 11 became a defining event the way Pearl Harbor had been for an earlier generation. President George W. Bush promised that the United States would make no distinction between the terrorists who carried out the attacks and those who harbored them — this became the foundation of the Bush Doctrine, holding that the United States had the right to act militarily against states that supported or provided sanctuary to terrorist organizations.

Congress authorized the use of military force within weeks. When the Taliban government of Afghanistan refused to surrender Osama bin Laden, the United States launched military operations in October 2001. Working with Afghan opposition forces, U.S. troops rapidly dismantled the Taliban government and drove al-Qaeda from its training camps. But bin Laden escaped into the mountainous border region between Afghanistan and Pakistan.

At home, the attacks produced a sweeping reorganization of government. Congress passed the USA PATRIOT Act in October 2001 with overwhelming bipartisan support, expanding the ability of law enforcement and intelligence agencies to conduct surveillance of suspected terrorists and loosening restrictions on information-sharing between agencies. Civil liberties advocates warned that the law gave the government dangerous powers to monitor citizens without adequate oversight. In November 2002, Congress created the Department of Homeland Security, consolidating twenty-two federal agencies and approximately 170,000 employees — the largest reorganization of the federal government since 1947.

The attacks had devastating consequences for Muslim Americans, Arab Americans, South Asian Americans, and Sikh Americans. Despite the fact that the vast majority of these communities had no connection to terrorism and that many were themselves victims of September 11, they faced a wave of discrimination, harassment, assault, and murder in the weeks that followed. The legal architecture of the War on Terror also included provisions that tested democratic norms and international law. The Bush administration created a detention facility at Guantanamo Bay, Cuba, to hold suspected terrorists outside the reach of U.S. courts. Detainees were held without charge, without trial, and without access to lawyers for years. The Supreme Court repeatedly pushed back: in Hamdi v. Rumsfeld (2004), the Court held that even enemy combatants who were U.S. citizens were entitled to due process; in Boumediene v. Bush (2008), the Court held that Guantanamo detainees had a right to habeas corpus.

The administration's counterterrorism program also included the use of "enhanced interrogation techniques" — including waterboarding — against detainees at secret CIA black sites. A Senate Intelligence Committee report released in 2014 concluded that the CIA's interrogation program was brutal, ineffective, and based on false claims about its usefulness.

The wars that followed September 11 defined the opening decades of the twenty-first century for American military personnel and for the populations of Afghanistan and Iraq. These wars were the longest in American history, consuming trillions of dollars, killing thousands of American service members and hundreds of thousands of civilians, and producing results far different from what their architects had promised.

The initial U.S. military campaign in Afghanistan achieved its immediate tactical objectives rapidly. The Taliban government collapsed within weeks. But the primary target — Osama bin Laden — escaped at Tora Bora in December 2001 when a decision to rely primarily on local Afghan forces allowed him to flee into Pakistan, where he would live for nearly a decade before being killed by U.S. Navy SEALs in Abbottabad in May 2011. The United States built a new Afghan government around Hamid Karzai. But the new government faced enormous challenges: a country devastated by decades of war, endemic corruption, a resilient Taliban movement regrouping in Pakistan, and a limited U.S. commitment to the nation-building that stable governance would have required.

The Taliban insurgency grew through the mid-2000s. President Obama ordered a surge of thirty thousand additional troops in 2009, adopting a counterinsurgency strategy. The surge produced temporary security gains in some areas, but the Taliban proved resilient. The fundamental problem was political: the Afghan government never achieved the legitimacy or capacity to stand on its own. After twenty years — the longest war in American history — President Biden completed the withdrawal in August 2021. The result was rapid collapse: the Afghan government and military disintegrated within weeks as Taliban forces swept across the country. On August 15, 2021, Taliban fighters entered Kabul. More than 2,300 American service members had been killed; the United States spent more than two trillion dollars. The Taliban returned to power governing much as they had before — banning women from schools and public life.

The war in Iraq was different in character: a war of choice, not necessity, whose justification proved to be false. The Bush administration argued that Saddam Hussein's government possessed weapons of mass destruction and had connections to al-Qaeda. Secretary of State Colin Powell made the case for war to the United Nations Security Council in February 2003 in a presentation later shown to rest on false and unreliable intelligence. Powell himself would call it a "blot" on his record.

The United States invaded Iraq in March 2003. The initial military campaign was swift — Saddam Hussein's government collapsed within weeks. But U.S. forces found no weapons of mass destruction. The postwar administration of Iraq made catastrophic decisions: dissolving the Iraqi army, dismissing Ba'ath Party members from government positions, and imposing economic policies that produced mass unemployment and resentment. Within months, a complex insurgency had emerged. The country descended into sectarian violence. By 2006, the situation had deteriorated into what many described as civil war. American casualties mounted. The U.S. public, which had initially supported the war, turned against it as the justifications proved false and the costs grew.

President Bush ordered a surge of approximately thirty thousand additional troops in 2007, accompanied by a new counterinsurgency strategy and the Anbar Awakening — an alliance with Sunni tribes who turned against al-Qaeda. Violence decreased significantly. But the underlying political problems remained unresolved. President Obama withdrew combat troops from Iraq in 2011. The withdrawal left a vacuum that contributed to the rise of the Islamic State (ISIS), which seized large areas of Iraq and Syria in 2013–2014, declaring a caliphate and carrying out mass atrocities. The United States launched a new military campaign against ISIS; the organization was largely defeated territorially by 2019 but continued to carry out attacks.

The Iraq War cost approximately 4,500 American military deaths, tens of thousands of wounded veterans, and an estimated two trillion dollars in direct costs. Iraq suffered far more severely — estimates of civilian deaths range from 100,000 to 600,000 or more, with millions displaced. The war destabilized the Middle East, strengthened Iranian influence in the region, and damaged American credibility worldwide. It left a profound debate about the use of military power, intelligence failures, executive authority, and the role of the United States in the world.

While U.S. forces fought in Afghanistan and Iraq, the American economy experienced a catastrophic collapse that would reshape politics for years. The Great Recession of 2007–2009 was the worst financial crisis the United States had experienced since the Great Depression. It destroyed trillions of dollars in household wealth, cost millions of Americans their jobs and homes, and exposed deep vulnerabilities in the financial system.

The crisis had its roots in the housing market and in financial innovations that had spread throughout the banking system over the previous decade. Banks and mortgage lenders had dramatically expanded the availability of home loans, including to borrowers with limited ability to repay them. These "subprime" mortgages were bundled into complex financial instruments — mortgage-backed securities and collateralized debt obligations — and sold to investors around the world. Rating agencies gave these instruments high credit ratings, understating the risk. When housing prices began to fall in 2006 and 2007, borrowers who had taken out adjustable-rate mortgages found their payments rising while their homes were worth less than they owed — a condition called being "underwater." Defaults rose. The value of mortgage-backed securities collapsed.

In September 2008, the crisis reached its acute phase. Lehman Brothers, one of the largest investment banks in the United States, filed for the largest bankruptcy in U.S. history at that time. The federal government was forced to rescue the insurance giant AIG, which had sold massive amounts of financial insurance instruments tied to mortgage-backed securities. Congress passed the Troubled Asset Relief Program (TARP) in October 2008, authorizing the Treasury to spend up to $700 billion to stabilize the financial system. The unemployment rate rose to 10 percent by October 2009 — the highest level since the early 1980s. More than eight million jobs were lost. Millions of Americans lost their homes to foreclosure.

Barack Obama took office in January 2009 in the middle of the crisis. The American Recovery and Reinvestment Act — approximately $787 billion in tax cuts, direct spending on infrastructure and state aid, and investments in renewable energy, education, and technology — passed without a single Republican vote in the House and with only three Republican votes in the Senate. The recovery was painfully slow. While the technical recession ended in June 2009, unemployment remained above 8 percent for years. Many workers who found jobs took lower-paying positions than those they had lost.

The Great Recession had deep political consequences. The bailout of major financial institutions — seen by many Americans as rewarding the bankers who caused the crisis while ordinary homeowners lost everything — generated anger across the political spectrum. The Tea Party movement, which emerged largely in response to government spending and the bank bailouts, drew heavily on this anger and pushed the Republican Party in a more populist, anti-establishment direction. On the left, the Occupy Wall Street movement of 2011 focused national attention on economic inequality, popularizing the language of the "99 percent" versus the "1 percent." Both movements reflected a deep sense that the political and economic system was rigged in favor of the wealthy and powerful — a sense that would fuel political upheaval for years to come.

Barack Obama's election on November 4, 2008, was a historic event in a nation whose history had been so deeply shaped by race. The son of a Kenyan father and a white mother from Kansas, raised in Hawaii and Indonesia, educated at Columbia and Harvard Law School, Obama had served as a community organizer, state senator, and U.S. senator from Illinois before his meteoric rise to the presidency. His campaign drew unprecedented enthusiasm, particularly among young voters, African Americans, and college-educated professionals. Obama carried states that had voted Republican for decades, winning 365 electoral votes and the popular vote by 7.2 percentage points.

Obama's first term was defined largely by the effort to pass healthcare reform. The Affordable Care Act, passed in March 2010 after a year of bitter legislative struggle, represented the most significant expansion of the American health insurance system since the creation of Medicare and Medicaid in 1965. The ACA created insurance exchanges, provided subsidies to help lower-income people afford coverage, expanded Medicaid, required insurers to cover people with pre-existing conditions, allowed young adults to remain on their parents' insurance until age 26, and imposed a requirement that individuals obtain insurance. The law was projected to extend coverage to more than 30 million previously uninsured Americans. Every Republican in Congress voted against it, and Republican-controlled states challenged it in courts. The Supreme Court upheld the individual mandate in National Federation of Independent Business v. Sebelius (2012), while ruling that states could opt out of Medicaid expansion — allowing Republican-governed states to leave millions of low-income adults without coverage.

Obama inherited two wars, a global financial crisis, and the counterterrorism architecture built after September 11. He authorized the operation that killed Osama bin Laden in Pakistan in May 2011 and negotiated the Iran nuclear deal — the Joint Comprehensive Plan of Action — with the United Kingdom, France, Germany, Russia, and China. In 2012, Obama was re-elected over Republican nominee Mitt Romney by a comfortable margin. His second term was marked by intense Republican opposition, including the government shutdown of 2013 and — most strikingly — the refusal of the Republican-controlled Senate to consider his nomination of Merrick Garland to the Supreme Court after Justice Antonin Scalia's death in February 2016. The Senate's refusal to hold hearings or a vote on Garland — unprecedented in its scope — illustrated the deepening dysfunction of the political system.

The Obama presidency raised profound questions about race in America. The killing of Trayvon Martin, an unarmed Black teenager, by George Zimmerman in 2012, and Zimmerman's acquittal in 2013, prompted Alicia Garza, Patrisse Cullors, and Opal Tometi to create the Black Lives Matter movement. The killing of Michael Brown in Ferguson, Missouri, in 2014, and the subsequent protests and grand jury decision not to indict the officer who killed Brown, brought racial injustice and policing to the center of national debate. The birther movement — which falsely claimed Obama was not born in the United States — drew support from millions of Americans and was promoted most prominently by Donald Trump. Obama left office in January 2017 with an approval rating in the high fifties, having presided over economic recovery, healthcare expansion, and the end of combat operations in Iraq — but having not resolved, and in some ways deepened, the political polarization that would define the years that followed.

Donald Trump's election in November 2016 was one of the most unexpected and consequential events in modern American political history. A real estate developer and television personality with no government experience, Trump defeated sixteen experienced Republican primary candidates and then defeated Hillary Clinton, the Democratic nominee and former secretary of state, senator, and first lady. Trump won the Electoral College 306 to 232 while losing the popular vote by nearly three million votes.

Trump's rise was rooted in forces that had been building for years. Economic anxiety among white working-class voters in economically distressed communities was central. Deindustrialization had hollowed out manufacturing regions, opioid addiction had devastated rural communities, wages had stagnated for workers without college degrees, and the Great Recession had left lasting scars. Cultural anxiety was equally important. Demographic change — the country's increasing diversity, driven by immigration and higher birth rates among nonwhite populations — unsettled many white voters who feared losing economic and cultural status. The legalization of same-sex marriage in 2015, the prominence of transgender rights debates, and the perceived dismissal of traditional values by coastal elites all contributed to a sense that their country was changing too fast and that they had no voice.

Trump's campaign was built on a form of populism that identified a corrupt elite — financial, political, and media — as the enemy of ordinary Americans. His slogan, "Make America Great Again," implied that the nation had been degraded and needed restoration. He promised to build a wall on the southern border, to ban Muslim immigration, to renegotiate trade deals, to withdraw from international agreements, and to "drain the swamp" of Washington corruption. His rhetoric was often inflammatory and contemptuous of democratic norms. He attacked journalists as "enemies of the people" and encouraged supporters to view political opposition as not merely mistaken but as treasonous.

Trump's presidency reshaped American governance and political culture in fundamental ways. He withdrew the United States from the Paris Climate Agreement, the Trans-Pacific Partnership, the Iran nuclear deal, and the World Health Organization. He imposed tariffs on goods from China, Canada, Mexico, and Europe. He cut corporate taxes through the Tax Cuts and Jobs Act of 2017. He appointed three conservative justices to the Supreme Court — Neil Gorsuch, Brett Kavanaugh, and Amy Coney Barrett — fundamentally shifting the court's ideological direction for a generation. His administration pursued aggressive immigration enforcement, including separating migrant children from their parents at the southern border and sharply reducing refugee admissions.

Trump was impeached twice by the House of Representatives: first in December 2019, for pressuring Ukraine's president to announce an investigation of Joe Biden in exchange for military aid; and second in January 2021, for incitement of insurrection related to the January 6 attack on the Capitol. He was acquitted by the Senate both times.

Joe Biden, who had served as a senator from Delaware for decades and as vice president under Obama, entered the presidency at age 78 — the oldest person ever inaugurated. His campaign had been built primarily around the argument that Trump was an existential threat to American democracy and that Biden's experience, temperament, and decency made him the right candidate to restore normalcy. Biden's victory in November 2020 was confirmed by every state, certified by the Electoral College, and affirmed by more than sixty court decisions. He won the popular vote by more than seven million votes.

Biden's first year in office produced a substantial legislative record. The American Rescue Plan, passed in March 2021, provided $1.9 trillion in economic relief: direct payments to households, expanded unemployment benefits, support for schools and local governments, and funding for vaccine distribution. The relief package contributed to rapid economic recovery — unemployment fell sharply, and the economy grew at the fastest rate in decades. But it also contributed to inflation, which rose to levels not seen since the early 1980s. The Federal Reserve responded by raising interest rates sharply beginning in 2022, slowing the economy and raising mortgage and consumer borrowing costs.

In August 2021, Biden signed the Infrastructure Investment and Jobs Act — a bipartisan bill providing approximately $550 billion in new spending on roads, bridges, broadband internet access, water systems, the electrical grid, and public transit. In August 2022, the Inflation Reduction Act provided approximately $369 billion for climate and energy investments — the largest climate policy action in U.S. history. Russia's invasion of Ukraine in February 2022 became a defining foreign policy challenge. Biden rallied NATO allies to support Ukraine with weapons, economic aid, and sanctions against Russia — widely praised as effective multilateralism and a restoration of the alliance-based foreign policy that Trump had eroded.

In July 2024, Biden made the extraordinary decision to withdraw from the presidential race, citing concerns about his ability to campaign effectively. Vice President Kamala Harris became the Democratic nominee — the first woman and first person of South Asian descent to be nominated for president by a major party. Harris lost to Trump in November 2024, and Trump was inaugurated for a second term in January 2025 — the first person since Grover Cleveland to serve non-consecutive presidential terms. The second Trump term brought renewed efforts to reshape the federal government, reduce immigration, roll back regulations, and assert expanded executive power.

Few developments have transformed American political and social life in the twenty-first century as profoundly as the rise of social media. The platforms that emerged in the 2000s and 2010s — Facebook (2004), YouTube (2005), Twitter (2006), Instagram (2010), Snapchat (2011), TikTok (2018 in the United States) — created entirely new ways for people to communicate, organize, consume news, and engage with political life.

Social media arose in a context of deep structural change in the traditional news industry. Thousands of local newspapers closed. Newsrooms shrank dramatically — the number of newspaper journalists fell by more than 57 percent between 2008 and 2020. Communities lost local reporting on city councils, school boards, county courts, and state legislatures — the kind of watchdog journalism that had held local government accountable for generations. Into this vacuum came social media, but with fundamentally different incentives than traditional journalism. Social media platforms were built around advertising revenue tied to user engagement. The algorithms that determined what content users saw were optimized for engagement, not accuracy. Research consistently showed that emotionally provocative content — outrage, fear, disgust — generated more engagement than calm, informative content. The result was a media environment that systematically rewarded sensationalism, polarization, and conflict over nuance and accurate information.

A landmark 2018 study published in Science found that false news stories spread on Twitter six times faster than true ones, and reached far more people. This was not primarily the product of automated bots; it was the product of human sharing behavior. Conspiracy theories gained unprecedented reach. QAnon — which falsely claimed that Trump was fighting a secret war against a network of satanic pedophiles in the deep state and Democratic Party — reached millions of Americans, with devastating effects on family relationships and, in some cases, motivating violence. Anti-vaccine misinformation spread widely and contributed to vaccine hesitancy that cost lives during the COVID-19 pandemic. Election fraud conspiracy theories, amplified by Trump and his allies, convinced millions of Americans that the 2020 election had been stolen.

The U.S. intelligence community concluded that Russia had conducted an information warfare campaign in the 2016 election, using fake accounts and targeted advertising on social media to inflame political divisions, suppress turnout among minority voters, and promote Trump's candidacy. Social media companies struggled to detect and remove foreign influence operations. When Elon Musk purchased Twitter in 2022 — renaming it X — and reinstated accounts that had been banned for policy violations, including Trump's account, the move illustrated the degree to which control of information infrastructure had become a political battleground. The debate over platform responsibility, content moderation, and free speech in the digital age remained one of the most pressing unresolved policy questions of the era.

The twenty-first century was a period of intense struggle over rights — over who was included in the American community, who was protected by law, and how the constitutional commitments of the nation applied to previously excluded or marginalized groups. These struggles produced major gains and intense backlash, often simultaneously.

The killing of unarmed Black Americans by police officers became a recurring crisis that catalyzed mass protests and a national reckoning with racial inequality. George Floyd's death on May 25, 2020 — pinned under the knee of Minneapolis police officer Derek Chauvin for more than nine minutes while bystanders pleaded with officers to stop — sparked the largest racial justice protests in American history. Protests erupted in hundreds of cities across the United States and in dozens of countries around the world. The diverse, multiracial character of the protests was notable. Chauvin was convicted of murder and sentenced to more than twenty years in prison — an unusually strong accountability outcome in a system that had historically rarely held officers criminally responsible for killing Black people.

The LGBTQ+ rights movement achieved remarkable gains, particularly in the recognition of marriage equality. The Supreme Court's ruling in Lawrence v. Texas (2003) struck down state laws criminalizing same-sex sexual activity. In 2015, the Court's decision in Obergefell v. Hodges held that the Constitution's guarantee of equal protection and due process required states to recognize same-sex marriages — the product of decades of organizing, litigation, cultural change, and shifting public opinion. Polls showed that support for same-sex marriage had risen from around 27 percent in 1996 to more than 60 percent by 2015. Transgender rights became a major site of political conflict in the 2010s and 2020s. Republican-controlled legislatures passed numerous laws restricting transgender people's access to medical care, sports, bathrooms, and legal documentation.

Immigration remained one of the most contested political issues of the era. The approximately eleven million undocumented immigrants in the United States lived in legal limbo, subject to deportation and ineligible for most federal programs. The Deferred Action for Childhood Arrivals program, created by Obama in 2012, provided temporary protection and work authorization to approximately 800,000 young people who had been brought to the United States as children. Migration at the southern border increased substantially through the late 2010s and early 2020s, driven by violence, poverty, climate change, and economic instability in Central America and other regions. The immigration system, designed for different patterns of migration, struggled to process large numbers of asylum seekers.

The Supreme Court's 2022 decision in Dobbs v. Jackson Women's Health Organization overturned Roe v. Wade (1973) and Planned Parenthood v. Casey (1992), eliminating the federal constitutional right to abortion and returning the question to individual states. More than a dozen states moved quickly to ban or sharply restrict abortion. The decision provoked immediate political backlash: voters in multiple states approved ballot measures protecting abortion rights, signaling that the public was significantly more supportive of abortion access than the court's ruling suggested. The decision became a central mobilizing issue for Democrats in the 2022 midterm elections, contributing to Democratic performance that exceeded most predictions.

Three structural challenges confronted the United States in the twenty-first century that demanded sustained policy responses but that political polarization made extremely difficult to address: climate change, public health, and economic inequality. Each represented not a single crisis but a systemic condition with long-term consequences.

The scientific evidence for human-caused climate change was overwhelming by the early twenty-first century. Average global temperatures had risen approximately 1.1 degrees Celsius above pre-industrial levels by the early 2020s. Extreme weather events — including hurricanes, wildfires, droughts, floods, and heat waves — were increasing in frequency and severity. The United States took inconsistent policy steps. The Obama administration negotiated the Paris Climate Agreement in 2015. Trump withdrew the United States from the agreement in 2017; Biden rejoined it in 2021. The Biden administration's Inflation Reduction Act of 2022 represented the largest investment in climate policy in U.S. history, directing approximately $369 billion over a decade toward clean energy, electric vehicles, building efficiency, and climate resilience. But the scale of the investment, while historically significant, fell short of what many scientists argued was necessary to meet the goals of the Paris Agreement. Climate change disproportionately affected low-income communities and communities of color, who had fewer resources to prepare for disasters or recover from them.

The COVID-19 pandemic, caused by the SARS-CoV-2 coronavirus, emerged in Wuhan, China, in late 2019 and spread globally in early 2020. The federal government's response under the Trump administration was widely criticized as slow, disorganized, and characterized by mixed messages on measures such as mask-wearing and social distancing. Vaccines developed at unprecedented speed received emergency authorization in December 2020. The Biden administration orchestrated a massive vaccination campaign in 2021. But vaccine hesitancy — fed in part by misinformation spread on social media and politically correlated with partisanship — meant that tens of millions of Americans refused or delayed vaccination, contributing to continued transmission and preventable deaths. The pandemic killed more than one million Americans by 2022, with Black, Latino, and Native American communities experiencing significantly higher rates of death, reflecting pre-existing inequalities in healthcare access, housing density, and the ability to work from home.

Economic inequality remained one of the defining challenges of the twenty-first century. By the 2020s, the wealthiest one percent of Americans held approximately 38 percent of all household wealth, while the bottom fifty percent held approximately 2 percent. The share of national income going to workers in the form of wages had declined relative to the share going to capital over the previous four decades. The causes were complex: the decline of union membership from approximately 35 percent of the workforce in the mid-1950s to approximately 10 percent by the early 2020s; the globalization of manufacturing; technological changes that increased demand for highly educated workers while reducing demand for lower-skilled ones; and deliberate policy choices about taxation, worker protections, and the social safety net.

The opioid epidemic, which began with the overprescription of legal opioids and evolved into a crisis of heroin and fentanyl addiction, killed hundreds of thousands of Americans and devastated communities across the country. Researchers Anne Case and Angus Deaton documented what they called "deaths of despair" — drug overdose, suicide, and alcoholism — concentrated in economically distressed communities and contributing to declining life expectancy among less-educated white Americans in the 2010s. These patterns were not inevitable; they were the product of policy choices, economic transformations, and failures of the social safety net that left communities without the resources to withstand economic disruption.

What changed across the long span of American history? The formal scope of American democracy changed dramatically over two and a half centuries: the franchise expanded from propertied white men to all citizens regardless of race, gender, or language. The federal government grew from a small administrative apparatus to a massive institution touching nearly every aspect of American life. Communications technology transformed from pamphlets and town meetings to instantaneous global digital networks. The United States became the world's dominant military and economic power.

What stayed the same? Persistent tensions that defined the founding era continued into the twenty-first century: the tension between federal and state power; the tension between liberty and equality; the tension between democratic self-government and the protection of individual rights from majorities; the tension between inclusion and exclusion; the tension between national interest and international responsibility. Economic inequality, far from being a new problem, had been a feature of American society since the colonial era. The question of who belonged in the American community — and on what terms — had never been fully resolved.

Understanding continuity and change helps resist two temptations: the temptation to see American history as inevitable progress toward a better future, and the temptation to see it as permanent oppression with no room for meaningful change. Both are distortions. The history shows real progress — in rights, in living standards, in inclusion, in the scope of democracy — alongside real regression, persistent inequality, and the chronic vulnerability of gains to reversal. That combination is the essential character of the American democratic experiment.

This chapter has examined the United States in the twenty-first century — a period of transformation, crisis, and renewed conflict over the fundamental questions that have defined American history from the beginning. The story of these decades is not simply the story of presidents, elections, or wars, though all of those matter. It is the story of ordinary Americans living through extraordinary times: of soldiers and their families navigating the longest wars in American history; of workers losing jobs, homes, and futures in the Great Recession; of Black families living with the ongoing reality of racially motivated police violence; of immigrant communities living in fear of deportation; of young people inheriting a planet in ecological crisis and a political system apparently unable to respond to it at the scale required.

The twenty-first century has tested the durability of American democratic institutions in ways that would have seemed extreme to earlier generations. The January 6 attack on the Capitol, the refusal of a sitting president to accept election results, the rapid spread of conspiracy theories and misinformation, the escalating partisan conflict over the most basic features of governance — all of these represent stresses on the system that the founders never anticipated, even as they built a system designed to withstand precisely the abuse of power they feared. The institutions held — but their holding was not inevitable, and it cannot be taken for granted in the future.

At the same time, this period has witnessed remarkable democratic energy. Mass movements for racial justice, environmental protection, LGBTQ+ equality, women's rights, and immigrant rights have demonstrated that American civil society retains extraordinary capacity for mobilization. The legalization of same-sex marriage, the expansion of health insurance coverage, the passage of major climate legislation — all achieved against formidable opposition — show that democratic change remains possible even in an era of intense polarization. These achievements were won through the same combination of organizing, advocacy, litigation, electoral politics, and cultural change that drove every previous expansion of rights in American history.

The history of the United States, traced across forty-eight chapters of this textbook, is a long argument about what kind of nation the United States should be. That argument has never been resolved — it has only taken different forms in different eras. The founders argued about it in Philadelphia in 1787. Abolitionists and slaveholders argued about it in the antebellum decades. Union and Confederate soldiers fought about it on the battlefields of the Civil War. Suffragists, civil rights marchers, labor organizers, and immigrant communities have all joined that argument in their own ways. The argument continues today, in courtrooms and legislatures, in streets and on social media, in elections and in movements. The United States remains, as it has always been, a nation whose future is not written — a nation whose promise is perpetually contested, perpetually unfinished, and perpetually open to those willing to do the work of democratic citizenship. That work is yours to continue.