Complex sentence: The largest number of clubs to have competed in the league was 18, in 2007 and 2008; however, during the recent 2011 season, there were 11 teams divided into two conferences, Red and Blue.
Split into simpler sentences: The largest number of clubs to have competed in the league was 18, in 2007 and 2008. In the 2011 season, the 11 teams were divided into two conferences, Red and Blue.