Complex sentence: He exhibited at the Worcester Art Museum in 1939 as a one man show but he was never able to successfully establish himself as an artist in the US, continuing to fill sketchbooks and make watercolor paintings.
Split into simpler sentences: He exhibited at the Worcester Art Museum in 1939 as a one man show. He was never able to successfully establish himself as an artist in the US, but he continued to fill sketchbooks and make watercolor paintings.