The Civil War Period in the United States lasted from 1861 to 1865, marked by a conflict between the Northern states (the Union) and the Southern states (the Confederacy). The war primarily arose from tensions over slavery, states' rights, and economic differences. Key battles, such as the Battle of Gettysburg and the Battle of Antietam, shaped the course of the war. The war ended with the surrender of the Confederate forces in 1865, leading to the abolition of slavery through the 13th Amendment. The period also set the stage for the Reconstruction Era, a time focused on rebuilding the nation and integrating formerly enslaved people into society.