Answer:
Southerners supported the Kansas-Nebraska Act because it gave them the possibility to decide whether to allow slavery or not in their states, based on popular sovereignty.
Step-by-step explanation:
The Kansas-Nebraska Act was passed by the Congress on May 22, 1854. This law provided for the organization of the Kansas and Nebraska territories. The so-called Missouri Compromise of 1820 was also revoked and the inhabitants of both future states were given the opportunity to decide for themselves about the possible admission of slavery, in the name of self-government by the people or popular sovereignty. The law entered into force on May 30.
The author of the law was Stephen Douglas, senator for the Democratic Party from the state of Illinois. He hoped for a reconciliation of North and South, but opponents rejected the law as a concession to the southern slave states. The Republican Party, founded by opponents of the Kansas-Nebraska Act, strongly opposed the expansion of slavery. The party would soon dominate national politics. The whole controversy renewed the political interest of Abraham Lincoln, who was to be elected the first Republican president in 1860.