The stubbornness of the South to try to ward off all attempts to put slavery into question was self-defeating.
The slave-based agricultural economy may have been huge, it was crippled by debt and a lack of broader investment.
They became so focused that they doomed themselves to defend it to the death because in their mind there was no other way, so the more they got flak for the slavery issue the more stubbornly they tried to anchor it down, which lead to a brain drain where educated people and those with money to invest, who were not inclined to put it into more slaves and cotton, found their way North or even outside the US.
Slavery or nothing worked back in the 18th century and in the early years of the 19th century where the North was still strongly tied to the Southern economy. Civil War was nearly impossible because vast amounts of Northern money was tied into the South. This changed as the demographics and economic diversity of the North changed dramatically.
If the South's economy had managed to keep the pace there might not have been a Civil War, just a lot of angry shouting in the household and zero chance for reform leading to a perpetual stand off.
This myopic protection of slavery became a self-fulfilling prophecy. Every mention of slavery in the North meant more entrenchment, more blinkers and the closing down of more options.
Meanwhile the Northern states were blinded by their success, their economic growth and increased dominance in the US political and economic realm, they did not see the divide or even understand the South's precarious position. To them it was a matter of reform and the South would be better off.
The idea of reform was unthinkable in the South, it would lead to economic ruin, plain and simple.
Both sides failed to retain any meaningful dialogue and in the 1850's things came to a boil, where people could see only one option that would work for both sides, secession.
Lincoln would not have a secession and war were declared …