Which slavery related event occurred first

The Kansas-Nebraska Act allowed each territory to decide the issue of slavery on the basis of popular sovereignty. Kansas with slavery would violate the Missouri Compromise, which had kept the Union from falling apart for the last thirty-four years.

Explanation:

the mongolian invasion of china and central asia resulted in a disruption of the silk road as the chinese garrisons lost support from the chinese kingdoms which fell under the mongols. however, as the mongols established a formal dynasty in china, the successors of genghis khan restored the garrisons along the silk road allowing the safe travel caravans again.

where is the picture of the graph or table?