Answer: C. the proposal that the Nebraska Territory would decide for itself whether to allow slavery.
Explanation:
The concept of popular sovereignty states that only the residents of the territory can choose whether or not slavery is allowed.
The Kansas-Nebraska Act (1854), proposed by Stephen A. Douglas, stated popular sovereignty to recognize the settlers“ right to make that decision within the new state. This act raised rather than reduced sectional conflicts, leading to Bleeding Kansas, a period of violence foregoing the American Civil War.