Why was Buchanan nominated by the democrats?

Slavery was the

major issue in the 1856 election. Democratic Party candidate James

Buchanan endorsed popular sovereignty giving the power to determine

the legality of slavery to the inhabitants of the territory seeking

statehood, rather than to Congress. The Republican Party opposed

the extension of slavery into the territories. Buchanan warned that

if the Republicans won the election, their anti-slavery position

would lead to civil war. Buchanan won 19 states including all of

the southern states. Buchanan also won a few northern states

including Pennsylvania, New Jersey, Illinois and Indiana.