Complex sentence: In July 1990 there were believed to be as many as 80 active members in New York City and by October 1992, when their activities in Chinatown had diminished significantly, there were factions of the gang operating in Georgia and Canada.
Split into simpler sentences: In July 1990 there were believed to be as many as 80 active members in New York City. But by October 1992, when their activities in Chinatown had diminished significantly, there were factions of the gang operating in Georgia and Canada.