The kansas-nebraska act nullified the missouri compromise by

  Allowing slavery's spread to areas that had been free for more than 30 years.

Explanation:

The Kansas-Nebraska Act enacted by Congress in 1854. It granted popular sovereignty to the people in the Kansas and Nebraska territories, letting them decide whether they'd allow slavery.  In essence, this made the Kansas-Nebraska act a repeal of the Missouri Compromise of 1820, which had said there would be no slavery north of latitude 36°30´ except for Missouri.

After the passage of the Kansas-Nebraska Act, pro-slavery and anti-slavery settlers rushed into Kansas to try to sway the outcome of the issue, and violence between the two sides occurred.  The term "bleeding Kansas" was used because of the bloodshed.  Kansas and Nebraska ended up as free states, but the Kansas-Nebraska Act had allowed the possibility that slavery could become slave states.

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.

answer

the statement that best describes president carter’s attempt to free the hostages in iran is c. all of the attempts failed.

explanation

the operation eagle claw conducted by the united states armed forces was a failed mission which aimed to rescue 52 americans captured as hostages in the american embassy, tehran on 24/4/1980.the mission was authorized by president jimmy carter. the failures included;   obstacles in operation that included operational conditions challenges caused by sandstorms, hydraulic problems of one the helicopters and , mechanical failure of another helicopter that was identified as a cracked rotor blade and the crashing of another helicopter during mission abortion causing death of 8 service persons.