Complex sentence: By the late 1990s, however, the mall had fallen in favor among shoppers due to the expansion of the St. Louis Galleria in Brentwood, Missouri, and the mall's flagship Dillard's store closed in 2001.
Split into simpler sentences: By the late 1990s, however, the mall had fallen out of favor due to the expansion of the St. Louis Galleria in Brentwood, Missouri. The mall's flagship Dillard's store closed in 2001.