What legislation repealed the Missouri Compromise of 1820?

The Kansas-Nebraska Act, passed in 1854, is the legislation that repealed the Missouri Compromise of 1820. The Missouri Compromise had established a line at the latitude of 36°30', north of which slavery was prohibited in the Louisiana Territory. The Kansas-Nebraska Act introduced the concept of popular sovereignty, allowing the settlers of these territories to determine for themselves whether they would allow slavery. This directly contradicted the Missouri Compromise's provisions and effectively nullified it, leading to significant conflict in these territories, as pro-slavery and anti-slavery factions clashed over the future of slavery in Kansas and Nebraska.

The other choices do not repeal the Missouri Compromise. The Compromise of 1850 was a series of legislative measures aimed at resolving disputes over slavery and territories but did not specifically address or repeal the Missouri Compromise. The Fugitive Slave Act, part of the Compromise of 1850, dealt with the return of escaped slaves but did not challenge the Missouri Compromise's framework. The Ostend Manifesto was a proposal for the annexation of Cuba by the United States and is unrelated to the issues surrounding the Missouri Compromise or the Kansas-Nebraska Act.