A NATION DIVIDED Disputes over the extension of slavery bitterly divided the states in the 1850s. A grass-roots anti-slavery movement in the North turned into the Republican Party, which was founded in 1854 and rapidly became a national force. In 1856, the Republicans nominated for president John Charles Fremont, the soldier who explored and mapped much of the West, but he lost to Democrat James Buchanan.In 1860, the Republicans turned to Illinois lawyer Abraham Lincoln, who won thanks to a split in the Democratic Party over slavery. The Civil War broke out in April 1861, and many Democrats (known as "War Democrats") supported Lincoln's efforts to save the Union. In 1864, the Republicans called themselves the Union Party and chose a War Democrat, Andrew Johnson, as Lincoln's running mate. Lincoln was re-elected but assassinated April 14, 1865, five days after the war ended. Abraham Lincoln, left, gained national attention through his debates with the better-known Sen. Stephen Douglas, whom he then defeated for the presidency. [ PREVIOUS | NEXT ]