Final answer:
Kansas earned the nickname "Bleeding Kansas" due to the violent clashes between antislavery and proslavery advocates, highlighted by events such as the Sack of Lawrence and the Pottawatomie Massacre, leading to over 150 deaths during a series of conflicts that preceded the Civil War.
Step-by-step explanation:
The nickname "Bleeding Kansas" refers to a series of violent civil confrontations in the Kansas Territory between 1854 and 1859, which were part of the sectional conflict over the legality of slavery in the proposed state of Kansas. The passage of the Kansas-Nebraska Act, which allowed the residents to vote on whether they would be a free or slave state, led to this bloody conflict. Under popular sovereignty, both antislavery and proslavery advocates rushed to Kansas to try to affect the vote, resulting in widespread violence and chaos.
The situation escalated with events like the Sack of Lawrence, where proslavery forces attacked and looted the antislavery settlement of Lawrence, and the Pottawatomie Massacre, where radical abolitionist John Brown and his followers retaliated by killing five proslavery settlers. This period of violence was an indication that the sectional crisis between the North and the South was becoming a national crisis, symbolizing the intense conflict that would lead up to the Civil War.
John Brown's actions and the guerrilla warfare that followed contributed to over 150 deaths and signified a new direction for some who opposed slavery, showing that they were willing to use violence to fight against the institution of slavery. The events in Kansas became known as Bleeding Kansas due to the scale of violence and bloodshed, which would continue and even escalate during the Civil War, affecting the political and social atmosphere of the entire country.