Complex sentence: Reagan's presidency came during the decline of the Soviet Union and just ten months after the end of his term, the Berlin Wall fell, and on December 26,1991, nearly three years after he left office, the Soviet Union collapsed.
Split into simpler sentences: Reagan's presidency came during the decline of the Soviet Union. Ten months after the end of his term, the Berlin Wall fell, and on December 26,1991, nearly three years after he left office, the Soviet Union collapsed.