Complex sentence: Ballrooms across the United States hosted the most popular big bands of the day, with Chick Webb leading one of the most popular bands at the Savoy Ballroom, and it was with his orchestra that the teenaged Ella Fitzgerald first gained fame.
Split into simpler sentences: Ballrooms across the United States hosted the big bands of the day, and Chick Webb led one of the most popular at the Savoy Ballroom. It was with his orchestra that teenaged Ella Fitzgerald first gained fame.