How did the split of the Democratic Party affect the outcome of the 1860 election and the Southern states' decision to secede?
It enabled Lincoln to become president and prompted the Southern states to secede
Two candidates ran for the Democratic Party during the 1860 election, Breckinridge from Kentucky and Douglas from Illinois. Lincoln as a Republican candidate managed to win the election. Despite the official narrative, he had no intention to abolish slavery as he clearly stated in his inauguration address.
The South feared his tariffs that he wanted to impose in order to finance the building of the transcontinentla railroad. He indeed intended to force the South to pay 90% of the federal taxes in tariffs despite its representing 30% of the population. It was called the Morrill tariff.