The history of the United States from 1991 to 2008 began after the fall of the Soviet Union which signaled the end of the Cold War and left the U.S. unchallenged as the world's dominant superpower. The U.S. took a leading role in military involvement in the Middle East. The U.S. expelled an Iraqi invasion force from Kuwait, a Middle Eastern ally of the U.S., in the Persian Gulf War. On the domestic front, the Democrats returned to the White House with the election of Bill Clinton in 1992. In the 1994 midterm election, the Republicans gained control of Congress for the first time in 40 years. Strife between Clinton and the Republicans in Congress initially resulted in a federal government shutdown following a budget crisis, but later they worked together to pass welfare reform, the Children's Health Insurance Program, and a balanced budget. Charges from the Lewinsky scandal led to the 1998 impeachment of Clinton by the House of Representatives but he was later acquitted by the Senate. The U.S. economy boomed in the enthusiasm for high-technology industries in the 1990s until the NASDAQ crashed as the dot-com bubble burst and the early 2000s recession marked the end of the sustained economic growth.
In 2000, Republican George W. Bush was elected president in one of the closest and most controversial elections in U.S. history. Early in his term, his administration approved education reform and a large across-the-board tax cut aimed at stimulating the economy. Following the September 11 attacks in 2001, the U.S. embarked on the Global War on Terrorism, starting with the 2001 war in Afghanistan. In 2003, the U.S. invaded Iraq, which deposed the controversial regime of Saddam Hussein but also resulted in a prolonged conflict that would continue over the course of the decade. The Homeland Security Department was formed and the controversial Patriot Act was passed to bolster domestic efforts against terrorism. In 2006, criticism over the handling of the disastrous Hurricane Katrina (which struck the Gulf Coast region in 2005), political scandals, and the growing unpopularity of the Iraq War helped the Democrats gain control of Congress. Saddam Hussein was later tried, charged for war crimes and crimes against humanity, and executed by hanging. In 2007, President Bush ordered a troop surge in Iraq, which ultimately led to reduced casualties.