Answer:
The Kansas-Nebraska Act repealed the Compromise of 1820.
Step-by-step explanation:
The Kansas-Nebraska Act was a law passed by the US Congress on May 30, 1854. It formed the new Territories of Kansas and Nebraska, opened them for settlement, and provided the population of the newly formed territories to independently resolve the issue of legitimizing or prohibiting slavery. This law repealed the Missouri Compromise adopted by Congress in 1820, according to which slavery was prohibited in the territories west of the Mississippi River and north of 36° 30' S.
The adoption of this law upset the balance between the northern and southern states, which sought to establish control over new territories, which ultimately led to the Civil War. In 1861, Kansas became part of the Union as a free state, while Nebraska received the status of a state after the war, in 1867.