Kansas–Nebraska Act

The Kansas–Nebraska Act of 1854 made the territories of Kansas and Nebraska, allowing the states to vote on whether slavery was legal or not. This law canceled the Missouri Compromise, which declared that slavery was not legal in those areas. It was passed on May 30, 1854. The Kansas-Nebraska Act angered many in the North who considered the Missouri Compromise to be a long-standing agreement. In the pro-slavery South, it was strongly supported. 
After the Kansas-Nebraska Act was passed, pro-slavery and anti-slavery supporters rushed in to settle Kansas to affect the outcome of the first election held after the new law went into effect. Pro-slavery settlers carried the election but anti-slavery settlers claimed the results were fraudulent, and did not accept defeat. The resulting fighting in Kansas gave it the nickname "Bleeding Kansas".