The Democratic split was so severe during the 1860 elections that they ran two candidates for the presidency.
The Democrats' split had defeated their own party.
By 1860, the Democrats dealt with certaint big issues that they couldn't ignore and couldn't solve. Slavery and states' rights were at the forefront of democratic discussions, and eventually the party splitted down regional lines.
On the one hand, Northern Democrats were firmly believed that slavery should not expand into the western territories. On the other hand, Southern Democrats believed that slave owners should be able to take their slaves wherever they pleased,