Complex sentence: Operation Green Quest was a United States Customs Service-sponsored interagency investigative unit formed in October 2001 after the September 11 attacks, and concerned with the surveillance and interdiction of terrorist financing sources.
Split into simpler sentences: Operation Green Quest was a U.S. interagency investigative unit formed in October 2001 after the September 11 attacks. Sponsored by the United States Customs Service, it was concerned with the surveillance and interdiction of terrorist financing sources.