Gettin' busy here.
Can we agree that the Dred Scott decision was the fork in the road that eventually led to the Civil War?
Now, you'll say that proves it was about slavery.
I'll say you are absolutely wrong.
The summary:
Supreme Court. In Scott v. Sanford the Court states that Scott should remain a slave, that as a slave he is not a citizen of the U.S. and thus not eligible to bring suit in a federal court, and that as a slave he is personal property and thus has never been free.
The court further declares unconstitutional the provision in the Missouri Compromise that permitted Congress to prohibit slavery in the territories.
In fact, the compromise is already under assault as a coalition of political leaders—some slaveholders, others westerners who resent the federal government's ability to dictate the terms of statehood—claim that territorial residents should be able to determine on what terms they enter the union.
The decision in Scott v. Sanford greatly alarms the antislavery movement and intensifies the growing division of opinion within the United State. The newly-formed Republican Party, which opposes the expansion of slavery, vigorously criticizes the decision and the court.
Question of slavery? No. Question of law. The Southerners "won" this one, no matter how morally reprehensible their support of slavery.
Nonetheless, despite their "win" their Constitutional "rights" as slaveholders were continually ignored and the laws that support them were unenforced.
This, IMO, is what drove sucession. It was the failure of the rule of law. The Southerners were well educated men. Many of the Founders had Southern backgrounds. They knew what their ancestors had put into the Constitution and they knew their "rights" were being denied.
Now, you can "shoot the messenger" but look at it from the other side:
Had the Constitutional guarantees provided for slavery been enforced, would their have been sucession and Civil War? (And those guarantees were there, were validated in the Supreme Court and were all the Southerners were asking for.)
Highly unlikely.