Complex sentence: At that time, the United States was experiencing the Great Recession, that started from late 2007--2008 which caused a "demographic transformation" of the gated community, where 1,400-square-foot townhouses sold on average for $250,000.
Split into simpler sentences: At that time, the United States was experiencing the Great Recession. This caused a "demographic transformation" of the gated community, where 1,400-square-foot townhouses had once sold on average for $250,000.