The American Civil War began in the year 1861. It marked a pivotal period in American history, fought between the Northern states (Union) and the Southern states that seceded to form the Confederacy. The war was rooted in long-standing tensions over issues such as slavery, state sovereignty, and economic differences. Beginning with the attack on Fort Sumter in April 1861, the war lasted until 1865, leading to significant changes in the United States, including the abolition of slavery and the reaffirmation of federal authority.