Complex sentence: Wu School is the term applied to a group of painters of the Southern School during the Ming period of Chinese history, and was not an academy or educational institution, but instead was largely by artistic theory of its members.
Split into simpler sentences: Wu School is the term applied to a group of painters of the Southern School during the Ming period of Chinese history. It was not an academy or educational institution, but rather a group united largely by the artistic theories of its members.