Complex sentence: By the late 1980s and early 1990s its fortunes took a turn for the worse, with nearby Westfarms and The Shops at Buckland Hills malls both expanded and built, the center began to feel the effects of competition.
Split into simpler sentences: By the late 1980s and early 1990s, the mall's fortunes took a turn for the worse. With nearby Westfarms and The Shops at Buckland Hills malls both expanded and built, the center began to feel the effects of competition.