Answer:
The American Civil War, also known as the US Civil War or the War Between the States, was a conflict that took place from 1861 to 1865 between the northern states of the Union and the southern states that had seceded to form the Confederate States of America.
The main reason for the Civil War was the controversy over slavery and its expansion into new territories. The Southern states relied heavily on slave labor for their agricultural economy, while the Northern states had largely abolished slavery and were moving towards an industrialized economy. The issue of whether new states admitted to the Union would allow slavery or not was a major point of contention between the North and the South. The election of Abraham Lincoln, who opposed the expansion of slavery, further heightened tensions between the two regions.
However, it's important to note that the reasons for the Civil War were complex and multifaceted. Other factors that contributed to the outbreak of the conflict include economic differences between the North and the South, political disagreements over states' rights and federal authority, and cultural differences between the two regions. Nonetheless, the issue of slavery and its expansion was the primary cause of the conflict.