Complex sentence: She continued after World War II to establish a Center for World Peace at Delphi, Greece, and when rebuffed by Greek authorities, purchased a fifteenth-century castle named Castello di Rocca Siniblada north of Rome, which she used to support an artists colony.
Split into simpler sentences: She continued after World War II to try to establish a Center for World Peace at Delphi, Greece. When rebuffed by Greek authorities, she purchased Castello di Rocca Siniblada, a fifteenth-century castle north of Rome, which she used to support an artists colony.