Complex sentence: The next decade produced further research on U.S. involvement in the 1973 overthrow of Salvador Allende's elected government in Chile corroborated by the "fears" of socialism succeeding in America.
Split into simpler sentences: The next decade produced further research on United States (U.S.) involvement in the 1973 overthrow of Salvador Allende's elected government in Chile. The coup reinforced the American "fears" of socialism succeeding in America.