Answer:
b. Kansas-Nebraska Act
Explanation:
The Kansas-Nebraska Law was the law enacted in the United States, in 1854, for the creation of the states of Nebraska and Kansas, in territories of former French Louisiana, but in which some Indian tribes remained. It was promoted by senator and leader of the Democratic Party Stephen Arnold Douglas of Illinois.
The situation of the two states north of the line defined in the Missouri commitment meant that both should be states in which slavery was not allowed. However, the contiguity of Kansas with the slave state of Missouri and Senator Douglas's quest for southern support for a railroad in his state caused the law to include the provision that, to decide on the question of slaves, citizens could exercise "popular sovereignty" and, therefore, to be able to decide whether to be a slave state.
The discussion of the law and the subsequent voting caused strong conflicts between anti-slavery and pro-slavery, especially in Kansas, and the disappearance of the Whig party (divided between supporters of the Law in the south and those opposed to it in the north ), and the creation of the Republican party. In addition to the most determined antisclavists, those who opposed the expansion of slavery, although accepting it in some way, limiting its existence to the states where it already existed, were added to the new party. That position contrary to slavery, although not abolitionist, allowed the Republican party to be the dominant force in the north, and not lose the entire southern vote, and that its candidate, Abraham Lincoln, won the presidential elections in 1860.