Complex sentence: The CAWIU became more effective in its organizing due to the leadership of Sam Darcy, who became the organizer for District 13 (which included California, Nevada, and Arizona) of the Communist Party USA in 1931.
Split into simpler sentences: The CAWIU became more effective in its organizing due to the leadership of Sam Darcy. Darcy became the organizer for District 13 (which included California, Nevada, and Arizona) of the Communist Party USA in 1931.