Complex sentence: Since the 1920's, La Cosa Nostra had been involved in importing (heroin, cocaine, and marijuana) into North America.Since the 1930's, the organization had been transporting narcotics from the East Asia Golden Triangle and South America to Cuba and into Florida.
Split into simpler sentences: Since the 1920's, La Cosa Nostra had been involved in importing (heroin, cocaine, and marijuana) into North America. In the 1930's, the organization started transporting narcotics from the East Asia Golden Triangle and South America to Cuba and into Florida.