Complex sentence: Many of the stores in the mall in its first 20 years were outposts of Chicago retailers, including Chas A Stevens, Kroch's and Brentano's, and C.D. Peacock.
Split into simpler sentences: Many of the stores in the mall in its first 20 years were outposts of Chicago retailers. Some of these included Chas A Stevens, Kroch's and Brentano's, and C.D. Peacock.