Popular sovereignty is the political concept that the authority of a particular government is directly determined by the will and democratic agreement of the people it governs. The term gained popularity in the 19th century United States during the debate of slavery legality in U.S. territories.
In the 1850s, U.S. Senator Stephen A. Douglas used the concept of popular sovereignty to help push the Kansas Nebraska Act through Congress. The bill essentially allowed the people to decide if slavery should be legal in the Kansas territory. This controversial bill led to a series of violent confrontations known as Bleeding Kansas, where pro- and anti-slavery advocates to openly fought over how to handle slavery in the territory.