Which conflict was primarily fought over the issue of states' rights and slavery?

The Civil War was primarily fought over the issues of states' rights and slavery, making it the correct answer. This conflict, which took place from 1861 to 1865, was fundamentally rooted in the differing views between the Northern states, which were generally anti-slavery and supported a stronger federal government, and the Southern states, which held onto the institution of slavery and advocated for greater state sovereignty.

The debate over whether states could nullify federal laws and the right of states to govern themselves without federal interference became increasingly contentious, particularly as new territories were being added to the United States and the question of slavery's expansion arose. The culmination of these tensions led to the Southern states seceding from the Union, which directly sparked the Civil War.

In contrast, the other conflicts mentioned do not primarily center around these issues. The Revolutionary War was fought for American independence from British rule. The War of 1812 was largely focused on trade restrictions and maritime rights against Great Britain. World War II involved a struggle against fascism and the quest for global dominance, with no direct connection to states' rights and slavery within the American context.