Mizoram was established as a Union Territory in 1972 following the Northeast Areas (Reorganisation) Act, 1971, and later became the 23rd State of India in 1986 after the 53rd Amendment, while Arunachal Pradesh, formerly known as the North-East Frontier Agency, transitioned from a Union Territory in 1972 to the 24th State of India on February 20, 1987, post the 55th Amendment to the Indian Constitution.