Answer:
C. In 1861, the war between the Southern states and the U.S. government began.
Explanation:
This is the historical event that best fits the theme of "state vs. federal rights." In 1861, the American Civil War began. One of the main reasons why the war began was because of the tension between the two levels of government when it came to the question of slavery. The Southern states wanted to maintain this institution, and they resented the power that the federal government had and the fact that they had to obey it.