Why did the Democratic Party split during the election of 1860?

The Democratic Party split during the election of 1860 primarily due to irreconcilable differences over the expansion of slavery into Western territories.31

The conflict centered on two competing visions for the party's platform:

• Southern Democrats: Led by figures who supported the Dred Scott decision, they demanded federal protection for slavery in all territories. They advocated for a platform—often associated with the Alabama Platform—that would codify the right of slaveholders to bring enslaved people into any territory, effectively preventing Congress or territorial legislatures from prohibiting the institution.21
• Northern Democrats: Led by Stephen A. Douglas, they championed popular sovereignty, which held that the residents of each territory should decide for themselves whether to permit slavery.23

At the 1860 Democratic National Convention in Charleston, these factions could not reach a consensus. When Northern delegates rejected the Southern platform, many Southern delegates withdrew. This led to two separate nominations: Northern Democrats nominated Douglas, while Southern Democrats nominated John C. Breckinridge.213