Identify the primary cause of the U.S. Civil War.

The primary cause of the U.S. Civil War was slavery, specifically the enslavement of African Americans. This issue was at the center of economic, social, and political conflicts between the Northern and Southern states. The Southern economy depended heavily on agriculture, which relied on enslaved labor. In contrast, the Northern states were developing a more industrial economy that increasingly opposed slavery.

As tensions grew over the expansion of slavery into new territories and states, significant legislative acts such as the Missouri Compromise and the Kansas-Nebraska Act attempted to address the issue but ultimately heightened the conflict. The abolitionist movement in the North gained momentum, advocating for the end of slavery and drawing attention to the moral and humanitarian aspects of the issue.

The election of Abraham Lincoln in 1860, who was perceived as anti-slavery, served as a crucial turning point. Southern states seceded from the Union in response, fearing that their way of life and economic interests were under threat. This secession led to the formation of the Confederacy and ultimately ignited the Civil War. Thus, slavery was not merely a backdrop for the conflict but was fundamentally intertwined with the political and social fabric of the time, making it the main catalyst for the war.