Complex sentence: By the late 1950s, Brundage was increasingly concerned about what to do with his collection with his homes in Chicago and California so overwhelmed with art that priceless artifacts were kept in shoeboxes under beds.
Split into simpler sentences: By the late 1950s, Brundage was increasingly concerned about what to do with his collection. His homes in Chicago and California were so overwhelmed with art that priceless artifacts were kept in shoeboxes under beds.