Complex sentence: He was a member of the group known as I Giovani di Palazzo Carminati (the youths of Palazzo Carminati), which reacted against the prevailing style of the Italian Academy at the beginning of the 20th century.
Split into simpler sentences: He was a member of the group known as I Giovani di Palazzo Carminati (the youths of Palazzo Carminati). This group rejected the prevailing style of the Italian Academy at the beginning of the 20th century.