What events happened before the American Civil War?

Answer 1

Acquisition of vast new territories from Mexico.

The Missouri Compromise not practical for deciding whether California should be free or slave.

California allowed to join the Union as free soil.

To appease the South, Congress agreed to hunt down fugitive slaves and return them to their owners. This became an emotive issue in the North, enraging the Abolitionists, and arousing hostility from the huge readership of 'Uncle Tom's Cabin'.

Then, in the Supreme Court, the Chief Justice interpreted the badly-worded Constitution to mean that slavery was fully protected in all states of the Union. This appeared to invalidate the recent agreement between North and South to allow new territories to vote whether to become slave-states or free soil.

Finally, John Brown's attack on a Union arsenal to procure weapons for a slave-revolt increased Southern mistrust of the Abolitionist lobby in Congress.

Lincoln won the 1860 election as a Republican, South Carolina seceded from the Union, and Lincoln rejected the last attempted compromise because it would have allowed some extension of slavery.

The war was on.