Abraham Lincoln
While Abraham Lincoln certainly sided with the North to preserve the Union, he made many compromises with the South to discourage them from leaving the Union. The Missouri Compromise prohibited slavery in unestablished states but it allow for Missouri to keep their slaves. This idea was to basically "contain" slavery within the states where it is already established. The Kansas-Nebraska Act in a sense was a repeal of the Missouri Compromise because now in Nebraska and Kansas, popular sovereignty can determine whether slavery is legal in those states or not. Abraham Lincoln did not want war with the South, so he did everything he could preserve the Union without war. Unfortunately, Lincoln felt that he no choice but to fight the South to keep the states together.