The kansas-nebraska act nullified the missouri compromise by a. ending slavery in agreed-upon slave territories. b. allowing slavery's spread to areas that had been free for more than 30 years. c. allowing slavery in all states. d. abolishing slavery in slave states

The Kansas-Nebraska Act nullified the Missouri Compromise by A. ENDING SLAVERY IN AGREED-UPON SLAVE TERRITORIES.

The Kansas-Nebraska Act of 1854 allowed settlers to decide whether their state will allow slavery or not.

The Missouri Compromise of 1820 was done to maintain the same number of free-states and slave-states. Missouri wanted to become a part of the slave-state but its admission with create an imbalance to the proportion of free-states and slave-states. They decided under the compromise, that Missouri will be a slave-state while Maine (former part of Massachusetts) will be a free state. Bring the number of slave and free states at an equal 12 states each. 

Very useful. it is to learn because history repeats itself so learning about it those mistakes not happen again.