Complex sentence: St. Elizabeths Hospital was the first large-scale, federally-run psychiatric hospital in the U.S. It was founded by Congress in 1852, largely as the result of the efforts of Dorothea Dix, a pioneering advocate for people living wtih mental illnesses.
Split into simpler sentences: St. Elizabeths Hospital was the first large-scale, federally-run psychiatric hospital in the United States. The hospital was founded by Congress in 1852, largely as the result of the efforts of Dorothea Dix, a pioneering advocate for people living with mental illnesses.