Complex sentence: The organization began as a grass roots organization in 1991, then operated under the auspices of the Olympia Rainbow Center from 2000 while operating as an independent group with a committee and elected officers.
Split into simpler sentences: The organization began as a grass roots organization in 1991. By 2000, it began to operate under the auspices of the Olympia Rainbow Center while operating as an independent group with a committee and elected officers.