Several Northern states, exercising their states' rights, decided that they would NOT actively enforce the federal law which required the return of escaped slaves to their self-styled "owners".
The South disagreed, believing that the Federal fugitive slave law should preempt the Northern states' rights.
Thereupon the Southern states seceded in order to form a new federal government of their own, under which states were not free to make their own laws regarding slavery.
So yes! the Civil War originated as a states' rights issue. It's just that the North was the pro states' rights side........
Note, the seceding states used an unlawful method of seceding knowing the other states in Congress would rightfully defeat the lawful methods of secession.
And again, they disagreed because it wasn't "Federal Law", it was Constitutional Law. The US Constitution, you know, that thing that makes "The UNION", require all member states of the UNION to return fugitive slaves. It is a specific written clause in the US Constitution that requires this.
Not returning fugitive slaves is breaking the requirements of the Union.