In 1776, after 169 years of distant and undemocratic British rule, the 13 Colonies declared independence. With the Constitution of 1787, the United States of America's four million people embarked on a political experiment: a democratic republic with representation at the local, state, and federal levels—with a built-in balance among executive, legislative, and judicial branches. From 1861 to 1865, the union of the United States was tested by the Civil War; it survived after a great loss of life.

On September 11, 2001, America witnessed death not seen on its soil since the Civil War, when 3,025 people died as four passenger jets were hijacked and turned into terrorist bombs—crashing in New York, Pennsylvania, and Virginia. The images of a destroyed World Trade Center and damaged Pentagon had a momentous impact on the country, and the government launched a war on terror. In October 2001 the U.S. led a military campaign against terrorists in Afghanistan, driving the Taliban regime from power. In November 2002 the Department of Homeland Security was created to protect the nation against terrorist attacks. In March 2003 a U.S.-led coalition invaded Iraq, toppling Saddam Hussein's hostile dictatorship.