Abraham Lincoln in known universally as the president who finally ended slavery in the U.S., but not many people understand what his underlying beliefs regarding slavery and expansion truly were. Prior to the outbreak of the Civil War, the expansion of slavery was a deal breaking issue for southern states in congress. The balance of slave and free states was always carefully balanced so that no one side had an advantage in the Senate. For this reason, one could not talk of expansion without having to address slavery.
As a Republican representative, Lincoln was opposed to the expansion of slavery into the territories because he felt it violated our nations founding republican principals and more practically because it created a inequity in the workforce. He returned to congress in the wake of the Kansas-Nebraska Act because he felt strongly that locals should not be allowed to decide on issues regarding slavery. He spoke out strongly about his opposition in the wake of this law, explaining that slavery violated republican principals and promising to halt its march to the Pacific. He ran for Senate for the Whig party on this stance.
In one of his most famous speeches, Lincoln declared that, “a house divided cannot stand.” He meant that the country could not continue to allow slavery to expand into new states and territories, and he would oppose any such efforts.