Final answer:
The Kansas-Nebraska Act introduced by Stephen Douglas in 1854 created two territories, Kansas and Nebraska. The act applied the principle of popular sovereignty and repealed the 36° 30' line from the Missouri Compromise, leading to sectional conflict and the formation of the Republican Party. The option (A) is correct.
Step-by-step explanation:
The Kansas-Nebraska Act was a pivotal piece of legislation introduced by Stephen A. Douglas in 1854. The act created two territories, Kansas and Nebraska, and applied the principle of popular sovereignty, meaning that the residents of these territories would decide whether to allow slavery.
This act also repealed the 36° 30' line from the Missouri Compromise, which further fueled sectional conflict and contributed to the formation of the Republican Party. Therefore, option (A) is correct.