The American Civil War was fought primarily in the United States, with the majority of the fighting taking place in the Southern states. The war began in 1861, when seven Southern states seceded from the Union and formed the Confederate States of America. The Union loyalists in the remaining states, as well as some geographically western and southern states, remained loyal to the United States government. The war lasted for four years and resulted in a Union victory. The war was fought in a number of locations, including the Eastern Theater, the Western Theater, and the Trans-Mississippi Theater. The Eastern Theater was the most important theater of the war, and saw some of the heaviest fighting. The Western Theater was also significant, and saw fighting in a number of states, including Tennessee, Mississippi, and Arkansas. The Trans-Mississippi Theater was the least significant theater of the war, and saw fighting in a number of states, including Texas, Louisiana, and New Mexico.