Complex sentence: Bonci served in the Italian army during World War I, returing to America to tour for three seasons after the war; he again appeared at the Metropolitan, and sang in Chicago during the 1920-21 season.
Split into simpler sentences: Bonci served in the Italian army during World War I, returing to America to tour for three seasons after the end of the conflict. He appeared again at the Metropolitan, and sang in Chicago during the 1920-21 season.