Why was sectional compromise impossible in 1860, when such compromises had previously worked in 1820 and 1850?

Question

Since Lincoln had guaranteed to protect slavery in the states where it existed, why did the seven southern states secede as soon as he was elected?

Answer 1

There was wide spread famine in Europe around 1848. That is when my great-great-great grandfather came from Germany. It was also the time of the Great Potato Famine in Ireland. Refugees poured in the Northern states in the 1850's.
The Europeans had no taste for the practice of slavery. The Northern States with much enlarged populations were less inclined to compromise over slavery and other economic interests of the Southern States.
This also ties in with religion being a cause of conflict. The Northern clergy had become much more inclined towards speaking out against slavery.
In 1807 it became illegal to bring new slaves into the U.S. The Slave Trade was on the decline and the abolitionists were becoming stronger. It also brought no money to Yankee ships.