Complex sentence: In the 19th and early 20th centuries, Franklin Square was at the center of a fashionable residential neighborhood, but beginning in the 1920s, a series of events corresponding with the rise of the automobile began the decline of the Square and its surrounding neighborhood.
Split into simpler sentences: In the 19th and early 20th centuries, Franklin Square was at the center of a fashionable neighborhood in which to live. But beginning in the 1920s, a series of events corresponding with the rise of the automobile began the decline of the Square and its surrounding neighborhood.