The influential leader during the American Civil War against slavery was President Abraham Lincoln. Lincoln, who served from 1861 to 1865, is best remembered for his commitment to ending slavery and preserving the Union during the deeply divisive conflict. He led the nation through its Civil War and issued the Emancipation Proclamation in 1863, which declared all slaves in Confederate-held territory to be free. Lincoln's leadership helped pave the way for the eventual passage of the 13th Amendment, forever abolishing slavery in the United States and redefining the nation’s values and legal structure.