Wrong. The Republicans gained a majority in the House in 1858 and the Senate in 1860. The election results were known in November 1860. South Carolina seceded in December 1860. You think the South couldn't see the dominoes falling?
And do you think that the post electoral plans of the Republicans were not well known, given that they had run for election on them??
"What would have prevented it?"
No Republican majority, no secession. It really "is" that simple.
"The first successful mechanical cotton harvester wasn't introduced until the 1930's."
Being from the South, I am well aware of the history of mechanical cotton picking. Without the huge expenditure of money and resources sucked up by the war, technological development would almost certainly been accelerated.
Senate control would not have happened until March 1861, and the first session of the new Congress wouldn't have convened until December 1861. But regardless, your claim was secession occurred because Lincoln and the Republicans were waging economic war on the Southern states. Since, as I said, they didn't control the White House and Congress until after secession then how were they able to wage the economic war that led the Southern states to rebel?
A cotton picking machine was patented in 1850. Here is a link.