After the American Revolutionary War in the 18th century, federalism was established, with the bourgeoisie and plantation slave owners governing jointly. However, the north and south still went their own way: the south of the United States developed slavery based on a plantation economy, while the north developed capitalist employment.

By the middle of the 19th century, the contradiction between these two opposing social systems had developed to an irreconcilable point. Southern slavery became a major obstacle to American society and economy. In 1860, Lincoln, who was famous for calling for maintaining federal unity and opposing the expansion of slavery, was elected the 16th President of the United States. Southern slave owners felt that power was being sidelined, so they began to create divisions and deliberately launched rebellion. In early 1861, the "Southern States Alliance" was established in the South. On April 12, southern rebels shelled Fort Sumter, which was stationed by Union troops, openly provoking a civil war. On April 15, Lincoln was forced to declare the South a rebellious state and recruit 75,000 volunteers to fight to restore Union unity.

In contrast, the North had an absolute advantage in terms of number of states, population, industrial production, finance, transportation, military power, or political support. However, the federal army suffered frequent losses in the early stages of the war. This was because the Southern army came prepared and gained the initiative, and it was also because the Lincoln administration set aside the most sensitive issue of the preservation and abolition of slavery. In July 1861, the first battle took place in the city of Manassas, 40 kilometers away from Washington. The Union army was defeated by the smaller Confederate army and Washington almost fell. After that, the masses held demonstrations demanding the liberation of slaves, the allocation of land to farmers, and the rescue of the crisis.

In order to change this situation, the Lincoln government took two major reform measures in a timely manner. On May 20, 1862, the government promulgated the Homestead Act, and on September 22, the government promulgated the Emancipation Proclamation. After this, the situation of war underwent fundamental changes, and the Union Army gradually took the initiative in each battlefield.

In the summer of 1863, the Union army turned to counterattack. After winning the decisive victory at the Battle of Gettysburg from July 1 to 3, it captured Vicksburg in the lower reaches of the Mississippi River on July 4, destroying the offensive power of the Allied forces and completely turning the tide of the war. Later, the Union Army adopted a new strategy to actively attack. By the end of 1864, the South was almost paralyzed. In November 1864, Lincoln was re-elected president with an absolute majority, and the South's defeat was settled.

On April 3, 1865, Union troops captured Richmond. On April 9, General Robert Lee, Commander-in-Chief of the Confederate Forces, led 28,000 troops to surrender to the Union Army. The American Civil War ended with the victory of the North and the United States was restored.

The American Civil War was the second bourgeois revolution in American history. It smashed the biggest obstacle to American political and social development-slavery, thereby enabling the United States to prosper in the shortest possible time and become the largest capitalist country.