Complex sentence: Initially, Carl and his band played clubs like The Bottom Line in New York City, and the Roxy in Los Angeles, then joined the Doobie Brothers as opening act on their 1981 summer tour.
Split into simpler sentences: Initially, Carl and his band played clubs like The Bottom Line in New York City and the Roxy in Los Angeles. Thereafter he joined the Doobie Brothers as opening act for their 1981 summer tour.