Abraham Lincoln (February 12, 1809 – April 15, 1865) was President of the United States from March 4, 1861 to April 15, 1865. As an outspoken opponent of the expansion of slavery and a political leader in the western states, he won the Republican Party nomination in 1860 and was elected president later that year.

Lincoln helped preserve the United States by leading the defeat of the secessionist Confederacy in the American Civil War. He introduced measures that resulted in the abolition of slavery, issuing his Emancipation Proclamation in 1863 and promoting the passage of the Thirteenth Amendment to the Constitution in 1865.

Lincoln's leadership qualities were evident in his close supervision of the victorious war effort, especially his successful selection of Ulysses S. Grant and other top generals. Historians conclude he brilliantly handled the factions of the Republican Party by bringing the leaders into his cabinet and forcing them to cooperate. In crisis management, he defused a war scare with the United Kingdom (1861), he outmaneuvered the Confederacy and took control of the border slave states in 1861-62, and he managed his own landslide reelection in the 1864 presidential election.