Complex sentence: Maidstone United was formed in 1897 and played in various Amateur leagues such as the Corinthian, Athenian and latterly the Isthmian League before joining the Southern League, the major semi-professional league in southern England, in 1971/1972.
Split into simpler sentences: Maidstone United was formed in 1897 and played in various Amateur leagues such as the Corinthian, Athenian and the Isthmian League. They joined the Southern League, the major semi-professional league in southern England, in 1971/1972.