Final answer:
The Kansas-Nebraska Act, passed in 1854, divided the territory west of Iowa and Missouri and allowed for popular sovereignty on the issue of slavery. Stephen A. Douglas, in order to please southerners, also repealed the 36° 30' line from the Missouri Compromise.
Step-by-step explanation:
The Kansas-Nebraska Act was the legislation through which Stephen A. Douglas agreed to divide the territory west of Iowa and Missouri. This act, passed in 1854, created two territories - Kansas and Nebraska - and allowed the people in these territories to decide whether to adopt slavery through popular sovereignty. In order to please southerners, Douglas also repealed the 36° 30' line from the Missouri Compromise, which angered many northerners.