The fugitive slave act made it so runaway slaves weren't given a fair trial when caught, and anyone who finds one must return the slave. If that person doesn't return the slave, they will be punished.
The northern states however were not happy with the fugitive slave act, and passed laws to fight against the act. These laws were called "Personal Liberty Laws" and they gave runaway slaves a proper trial, causing expenses for the slave owner.
The Underground Railroad was also formed, which was a series of homes where anti slavery homeowners would take in slaves, feed them, hide them, and direct them to the next safe home on the trail to safety.
In 1854, the Kansas-Nebraska Act was passed, which gave Kansas and Nebraska the choice to become slave states, and repealed the Missouri Compromise which would have restricted this decision
People started moving into Kansas, most were proslavery but the anti-slavery people moved into the town of Lawrence.
Town of Lawrence
The state of Nebraska deemed the town of Lawrence as traitors, and a group of people went to burn down the town and kill a lot of people that were living there. People ran away, but others with guns stayed, and they fought back. This was how bleeding Kansas begun