Complex sentence: While still a teenager he embarked on a career as a concert violinist with the Warsaw Philharmonic under Julius Wertheim before returning to Chicago in 1920 to join the orchestra at Central Park Casino.
Split into simpler sentences: While still a teenager he embarked on a career as a concert violinist with the Warsaw Philharmonic under Julius Wertheim. He returned to Chicago in 1920 to join the orchestra at Central Park Casino.