The state of Tennessee is rooted in the Watauga Association, a 1772 frontier pact generally regarded as the first constitutional government west of the Appalachians. What is now Tennessee was initially part of North Carolina, and later part of the Southwest Territory. Tennessee was admitted to the Union as the 16th state on June 1, 1796. Tennessee was the last state to leave the Union and join the Confederacy at the outbreak of the U.S. Civil War in 1861. Occupied by Union forces from 1862, it was the first state to be readmitted to the Union at the end of the war.