Complex sentence: The song was the most popular number in first successful Broadway theater production to have an all African-American cast and broke what had been a taboo against musical and theatrical depictions of romantic love between African-Americans.
Split into simpler sentences: The song was the most popular number in first successful Broadway theater production to have an all African-American cast. The show and in particular the song broke what had been a taboo against musical and theatrical depictions of romantic love between African-Americans.