Definition
The American Civil War was the war fought from 1861 to 1865 between the United States — the Union — and eleven Southern states that broke away to form the Confederacy. Its central cause was slavery: the Southern states seceded to protect a society and economy built on enslaved labour, while the Union fought first to preserve the nation and increasingly to end slavery itself.
The conflict was the deadliest in American history, killing roughly six hundred thousand soldiers. It ended with the defeat of the Confederacy, the restoration of the Union, and the abolition of slavery throughout the country.
Why it matters
How it works
Civil wars erupt when a society splits over a question too fundamental to compromise away. In the United States, decades of failed compromises over the expansion of slavery had left the two regions with incompatible visions of the nation's future. The election of an anti-slavery-expansion president triggered secession, and secession triggered war. The Union's larger population, stronger industry, and railway network gradually wore down the Confederacy — a reminder that wars of attrition are often decided by economic capacity as much as by battlefield skill.