1776: Thirteen American colonies declare independence from Great Britain; the Constitution is signed in 1787 and takes effect in 1789.
19th Century: Westward territorial expansion, rapid industrialization, and the American Civil War (1861–1865), which preserves the Union and ends with the abolition of slavery (13th Amendment, 1865).
1917–1945: Pivotal intervention in World War I and World War II establishes the nation as an international military and economic power.
1947–1991: Leads Western allies through the Cold War against the Soviet Union while navigating the domestic 1960s Civil Rights Movement.
Late 20th–21st Century: Drives the global internet and digital technology revolutions as the world's largest economy by nominal GDP.