Complex sentence: Armitage won an international mural contest sponsored by David Alfaro Siqueiros, and in 1949, Armitage became Siqueiros's assistant, working on many murals on public buildings throughout Mexico.
Split into simpler sentences: Armitage won an international mural contest sponsored by David Alfaro Siqueiros, and in 1949, Armitage became Siqueiros's assistant. Armitage worked on many murals on public buildings throughout Mexico.