Final answer:
The American Civil War was primarily caused by the issue of slavery and its expansion into new territories, which led to conflict between the southern slave economy and the northern antislavery stance. Abraham Lincoln's election and Southern secession directly led to the Civil War, which brought profound changes to the United States both during and after the conflict.
Step-by-step explanation:
The Cause of the Civil War
One primary cause of the American Civil War was the contentious issue of slavery. As historian James McPherson notes, soldiers fought for cause and comrades, valuing liberty, freedom, and loyalty. The 1860 election of Abraham Lincoln also played a significant role. Lincoln's Republican Party's stance to prevent the expansion of slavery into new territories was a major threat to the Southern states, which relied heavily on a slave economy. Moreover, the Southern states favored a weaker central government that wouldn't interfere with their right to maintain slavery. These tensions, alongside Lincoln's election, sparked the southern secession and ultimately led to the formation of the Confederate States of America, igniting the Civil War.
Furthermore, the war brought considerable political, economic, and social changes. It reshaped the power balance between federal and state governments, transformed the economies of the North and South, and resulted in the emancipation of enslaved individuals. The Civil War represented a definitive moment in American history, signaling the end of slavery and redefining the nation's values and government structure.