Lincoln was in office from March 4, 1861 – April 15, 1865. He was re-elected in 1964 before being assassinated. Lincoln campaigned in 1860 against expansion of slavery and when he won election, 7 or so states seceded from the Union. Lincoln was the president of the USA the entire Civil War. So, in a way, he was leader of the north, but he was also technically president of the South as well. The South was trying to secede from the USA.