Who were the northern presidents before the US Civil War?

All of the Presidents of the United States up to and including Abraham Lincoln. The Civil War did not begin until after Lincoln took office, although several southern states had seceded following his election in November of 1860 and prior to his inauguration. Most historians consider the war to have begun when Confederate forces under P.G.T. Beauregard fired on Fort Sumter in Charleston harbor on 12 April 1861.

You could mean James Buchanan, who lost to Lincoln and did nothing more to stop the oncoming war.