The war fought between the Northern and Southern United States from 1861 to 1865 is known as the American Civil War. This conflict stemmed primarily from disagreements over slavery and states' rights, which led to significant sectional tensions. Southern states, seeking to maintain and expand the institution of slavery, seceded from the Union, forming the Confederate States of America. The war resulted in roughly 620,000 to 750,000 deaths, making it one of the deadliest conflicts in U.S. history. The Union's eventual victory preserved the United States and led to the abolition of slavery through the 13th Amendment.