Complex sentence: Beginning circa 1960 a fear of Communism dominated, in light of communist victories in China, Africa, Eastern Europe and Latin America, which took the form as a major militia movement concern of a collectivist takeover of the United States.
Split into simpler sentences: Beginning circa 1960, a fear of Communism dominated, in light of communist victories in China, Africa, Eastern Europe and Latin America. This became elevated as a major concern of the militia movement, fearing a collectivist takeover of the United States.