Answer:
1. The 1850 Compromise had broken down, and new solutions were being sought for the issue of slavery in the new states.
2. Stephen Douglas suggested that the issue should be put to the vote in each new state created. He called this 'Popular Sovereignty', and it was enshrined in the Kansas-Nebraska Act.
3. The Kansas territory was thinly-populated, and the vote was likely to be close. Strong believers from both sides moved in and bought cheap properties in order to qualify for the vote, and hopefully influence the result in their own favour. Indigenous Kansans called these new arrivals 'the squatters'.
4. There were also bully-boys from both sides who invaded the territory in order to intimidate voters and disrupt the polls. One of these was John Brown, who helped to cause the kind of bloodshed that gave rise to the name 'Bleeding Kansas'.
5. In due course, it was clear that Kansas had voted to be free soil. But 'Popular Sovereignty' had not worked well and was never tried again. 'Bleeding Kansas' was a grim reminder that the slavery issue would never be resolved through lawful debate.