Which war was primarily fought over issues of slavery and states' rights?

The Civil War was primarily fought over issues of slavery and states' rights, making it the correct answer. This conflict arose in the United States from the 1860s, primarily due to the deep-seated disputes between the Northern states, which were generally anti-slavery, and the Southern states, which advocated for the institution of slavery as essential to their agrarian economy. The war brought to the forefront the debate regarding states' rights, as Southern states argued that they had the right to govern themselves and make their own laws, including those that protected slavery. The culmination of these tensions ultimately led to secession of several Southern states and the outbreak of the Civil War in 1861. This war remains a pivotal moment in American history, fundamentally altering the nation’s social, political, and economic landscape.

In contrast, the Revolutionary War was fought primarily for independence from British rule, the War of 1812 focused on issues such as trade restrictions and territorial expansion against Britain, and World War I involved complex alliances and geopolitical conflicts in Europe, none of which were centered on slavery or states' rights in the way the Civil War was.