Complex sentence: He is known as the framer of the U.S. policy of "dual containment" which sought to'contain' Iraq and Iran, which were both viewed as the United States' two most important strategic adversaries at the time.
Split into simpler sentences: He is known as the framer of the U.S. policy of "dual containment" in that period, which sought to'contain' Iraq and Iran. These were viewed as the United States' two most important strategic adversaries at the time.