Complex sentence: The powerful trade unions, to maintain unity among the workers, successfully campaigned against the use of dialects: this allowed southerners, whose dialects were not mutually intelligible with the northerners', to integrate using Standard Italian.
Split into simpler sentences: The powerful trade unions successfully campaigned against the use of dialects to maintain unity among the workers. This allowed southerners, whose dialects were not mutually intelligible with the northerners', to integrate using Standard Italian.