Complex sentence: Provincially, the AMS is a founding member of the Ontario Undergraduate Student Alliance in 1992, however left the organization in 1995 but rejoined the organization in 2004 as full members after a number of years as associate observers.
Split into simpler sentences: Provincially, the AMS is a founding member of the Ontario Undergraduate Student Alliance (OUSA), and thus initially became a member in 1992; however, the AMS left the organization in 1995. In 2004, the AMS rejoined OUSA as full members, after a number of years as associate observers.