Complex sentence: In the 1920s Johnson moved to New York City where he became research director for the National Urban League and "entrepreneur of the Harlem Renaissance," the creative upsurge by African American writers and artists of that time.
Split into simpler sentences: In the 1920s Johnson moved to New York City, where he became research director for the National Urban League. He was an "entrepreneur of the Harlem Renaissance," the creative movement by African-American writers and artists of that time.