The American Civil War (1861-1865) was a pivotal conflict between the Northern states (Union) and Southern states (Confederacy) over issues including slavery, states' rights, and economic differences. The war began after the Southern states seceded from the Union following the election of President Abraham Lincoln, who opposed the expansion of slavery. Key battles like **Gettysburg** and **Antietam** defined the war, while Lincoln's **Emancipation Proclamation** in 1863 marked a turning point by making slavery abolition a Union goal. The war ended in 1865 with the Confederacy's defeat, leading to the abolition of slavery and significant social and political changes in the U.S.