Complex sentence: Dobbs was one of the initiators of a general strike in Minneapolis, and for a while worked full-time as a union organiser, but quit in 1939 to work for the new Socialist Workers Party (SWP).
Split into simpler sentences: Dobbs was one of the initiators of a general strike in Minneapolis, and for a while worked full-time as a union organizer. Dobbs quit in 1939 to work for the new Socialist Workers Party (SWP).