Complex sentence: In 2004, Albertsons, Inc. bought Sainsbury's American supermarket assets, including Star Market, after which Star Market and Osco Drug were reunited under one corporate umbrella.
Split into simpler sentences: In 2004, Albertsons, Inc. bought Sainsbury's American supermarket assets, including Star Market. When that happened, Star Market and Osco Drug were reunited under one corporate umbrella.