Complex sentence: The demise of this league saw Banstead join the Isthmian League in 1984, where they remained until May 2006, when they resigned from the league and joined the Combined Counties League from the 2006-07 season.
Split into simpler sentences: The demise of this league saw Banstead join the Isthmian League in 1984. However in May 2006 they resigned from this league and joined the Combined Counties League from the 2006-07 season.