What event made slavery a central political issue in the 1850s?

The decision to allow the people of Kansas to vote whether their new state would be slave or free.

This thinly-populated territory attracted all manner of cross-border raiders from both sides of the debate, determined to intimidate voters and get the results declared invalid.

There was terrible bloodshed, and it seemed to demonstrate that the slavery debate would never be resolved, except through combat.

The slave-question that caused the new Compromise of 1850 was the admission of California as free soil.

Lands were gained gained as a result of the Mexican-American War.

The emotive issue was the new, stricter version of the Fugitive Slave Act, which caused many Northerners to join the Abolitionist movement.