For the 1999–2000 season the league increased in size to 22 clubs when two clubs were promoted into the Alliance but none relegated out of it. One of the promoted clubs was Oadby Town of the Leicestershire Senior League, the first time a team from that league had been promoted into the Alliance. Two years later, the league increased in size to 23 clubs as more teams joined than left, but Stapenhill resigned midway through the 2001–02 season, reverting the number of clubs in the competition back to 22. The league expanded to 24 clubs for the 2003–04 season, at the end of which, for the first time, Alliance clubs were promoted to the Northern Premier League, rather than the Southern League, when Rocester and Willenhall Town joined the more northerly of the two leagues. The following season Coalville Town became the first Alliance team to reach the first round proper of the FA Cup, a feat which was repeated in the 2005–06 season by both Chasetown and Leamington.