Mmm hmm, sure. Yeah, that really unfair system that inflated Congressional representation for the South by counting 60% of the non-voting slaves and forced Northern states to round up and send back escaped slaves. That and tariffs (which you like now but didn’t like back then).
A bunch of rich slave owners wanting to preserve their power is why it happened, period. You play make beleive if you tell yourself otherwise. Protecting slave owners interests was the CSA’s ONLY reason for existence. If you still wanna wax nostalgic on the CSA more power to you, but you don’t get to deny facts. No one started a war over not liking GD Massholes.
The US Constitution specifically required that. If the Northern states refused to do it, it was breaking the agreement upon which the Constitution was conditionally ratified.
The section of the US Constitution which specifically required all states to return fugitive slaves is Article IV, Section 2.
You won't like it, but it is in there.