It began long before that. The New England states were, as usual, flexing their power muscles.
The first federal intervention was the Northwest Ordinance of 1787 that established the new territory located northwest of the Ohio Rivers. It established the admission protocol for future states. It addressed the slavery issue by declaring the Territory as free; however a fugitive slave law was also included.
This sounds like a good compromise on paper, but the South was not happy.
The federal government had, for the first time, addressed the slavery question instead of leaving it to the people. This was against the US Constitution’s limitation of powers, as the South saw it.
It also did not like the fugitive slave law. It set a bad precedent.
Most insidious of all, this established a way for New England to expand its power base because all of the future states were already proclaimed free. Future federal senators and representatives of the states would vote with New England.