The primary cause of the American Civil War from a political perspective was the contentious issue of slavery and its expansion into newly acquired territories. As the U.S. expanded westward, debates over whether new states would allow slavery heightened tensions between Northern abolitionists and Southern slaveholders. The Missouri Compromise and the Compromise of 1850 attempted to quell these conflicts but ultimately failed, leading to a series of heated political confrontations. The election of Abraham Lincoln in 1860, seen as a threat to slavery, triggered the secession of Southern states and the onset of the Civil War.