Answer:
Passage of the Kansas-Nebraska Act allowing Popular Sovereignty in the Kansas and Nebraska territories to decide on the slave issue.
Step-by-step explanation:
Bleeding Kansas refers to the time period where proslavery and anti-slavery supporters fought against each other in a small civil war. This war was a result of the power to control the new territory of Kansas.
With the passage of the Kansas-Nebraska Act in May 1854, the issue of the legality of slavery became a much-heated argument. This controversial confrontation opined that the principle of popular sovereignty allows the residents of Kansas to decide whether the area will be pro-slavery or anti-slavery. The confrontation led to the small but violent war which became known as "Bleeding Kansas".
Thus, the correct answer is the first option.