Basically, I want to know how to get the ACW to start in the early 1850s, possibly due to the failure (or non-existence) of the Compromise of 1850.
So, three questions for such a scenario:
1) What could lead to the *ACW occurring at this point? Would it work if I butterflied away Zachary Taylor's death?
No. For a long time it was widely believed that Taylor opposed the Compromise of 1850, and that only his death allowed it to go through. This idea was put forward in R. A. Billington's authoritative
Westward Expansion. It's one of the Great White Whales of AH.
Taylor took one position strongly opposed by the slavery advocates: for the immediate admission of California as a free state.
But more recent scholarship shows a more nuanced view. Taylor wanted California admitted because he worried about what could happen if the territory was left unorganized. He had been an Army commander on the frontier.
Beyond that, however, he had no strong feelings. As a Whig, he was pledged not to veto any legislation unless it was unconstitutional.
Also, there was a newspaper generally considered the adminstration mouthpiece, which editorialized in favor of the Compromise.
2) What might the course of the war look like?
3) What might the results be?
It's hard to see how there could have been a war at all. In 1860, Southerners were galvanized to support secession (by relatively narrow margins, initially) by the election of an openly anti-slavery President from the North, only a year after John Brown's attempt to foment slave rebellion. Taylor was himself a slave-owning Louisiana planter - he could not be portrayed as a threat. It's possible that South Carolina might have declared secession anyway. But no other state would, and Taylor was a strong nationalist. He would have sent the Army to suppress secession, and South Carolina would have submitted without fighting. Perhaps if the VP was someone else... Fillmore was chosen to "balance the ticket" and help carry New York. Perhaps if a different New Yorker was VP - William Seward! He was known to be anti-slavery. Billiington wrote that Taylor blocked the Compromise at the urging of Seward - which was wrong - but Seward was friends with Taylor, so he might have accepted the nomination. But even so - Southern opinion hardened considerably in the 1850s, and there was much less fear of slavery being subverted. Except in South Carolina, which would be out on their own if they dared to declare secession. I think one needs to have an earlier divergence.