The Framers struggled with balancing states' rights and the federal government's power as they crafted the Constitution. They also wrestled with the question of slavery.
They assumed (wrongly) that slavery would die out on its own. But for 75 years after the Constitution's ratification, slavery grew and spread into new territories, the exact opposite of what they'd expected.
Then came the Dred Scott case. Supreme Court Chief Justice Taney thought he could solve the slavery question once and for all from his bench.