Modotti introduced Guerrero to Stalinist thought and he became politically active with the communist movement. He became a lifelong supporter of socialist and communist politics. He founded the El Machete, a publication of the Mexican Communist Party along with David Alfaro Siqueiros in 1924 and the two also founded the Sindicato de Obreros Técnicos, Pintores y Escultores union. His work in politics and journalist took him to various parts of the world, including the Soviet Union, where he went in 1927 to attend the Lomonosov University.
