Complex sentence: In advance of World War II, in 1939, Feininger immigrated to the U.S. where he established himself as a freelance photographer and in 1943 joined the staff of "Life" magazine, an association that lasted until 1962.
Split into simpler sentences: In advance of World War II, in 1939, Feininger immigrated to the U.S. where he established himself as a freelance photographer. In 1943 he joined the staff of "Life" magazine, an association that lasted until 1962.