Complex sentence: In the 1930s, many exponents of this movement became irredentist, seeing as the only solution to the problems of the island annexation to fascist Italy, which under Benito Mussolini had become one of the main goals of Italy's imperialist policy.
Split into simpler sentences: In the 1930s, many exponents of this movement became irredentist, seeing annexation of the island to fascist Italy as the only solution to it's problems. Under Benito Mussolini annexation had become one of the main goals of Italy's imperialist policy.