U.S. territory expanded westward across the continent, brushing aside Native Americans and Mexico, and overcoming modernizers who wanted to deepen the economy rather than expand the geography. Slavery of Africans was abolished in the North, but heavy world demand for cotton let it flourish in the Southern states. The 1860 election of Abraham Lincoln calling for no more expansion of slavery triggered a crisis as eleven slave states seceded to found the Confederate States of America in 1861. The bloody American Civil War (1861–65) redefined the nation and remains the central iconic event. The South was defeated and, in the Reconstruction era, the U.S. ended slavery, extended rights to African Americans, and readmitted secessionist states with loyal governments. The present 48 contiguous states were admitted by early 1912.
The Soviet Union and the U.S. emerged as opposing superpowers after the war and began the Cold War confronting indirectly in an arms race, the Space Race, and intervention in Europe and eastern Asia.
Liberalism reflected in the civil rights movement and opposition to war in Vietnam peaked in the 1960s–70s before giving way to conservatism in the early 1980s. The Cold War ended when the Soviet Union dissolved in 1991, leaving the U.S. to prosper in the booming Information Age economy that was boosted, at least in part, by information technology. International conflict and economic uncertainty heightened by 2001 with the September 11 attacks and subsequent War on Terror and the late-2000s recession.




