Why is James Buchanan important?

James Buchanan is important because he was the last President before the Civil War. Tensions had been building up for some time between the slave states and the free states, but Buchanan, instead of showing leadership, failed to resolve those tensions. Instead, he showed blatant bias towards the Southern states, on whose votes he'd depended for his election in 1856.
In his final address to Congress, he failed to rise to the occasion and provide a way forward that could unite the country. Instead, he openly blamed Northern states for the rapidly developing crisis engulfing the nation, accusing them of interfering with Southern states' rights. At the same time, the South wasn't completely satisfied with Buchanan either, as he expressed his implacable opposition to secession, which they saw as the only way out of the impasse. For his inability to stop the country sliding towards civil war, Buchanan has gone down as one of the worst Presidents in American history, a judgement with which it's difficult to disagree.