Answer: Because Ronald Reagan program forced the Soviets to increase their budget in military and weapons expenses, unbalancing their economy and contributing to the fall of communism.
Step-by-step explanation:
Reagan started a program of a major buildup of nuclear and conventional weapons, in order to force Soviets to spend much more of their budget on their own military budget, and by doing this they would force the Soviets to their own bankruptcy. The program really had an effect on the Soviet side which launched an expensive research and development venture of their own to keep pace with the USA. By the end of Reagan's second term, we can point out some important achievements such as a remarkable arms-reduction agreement with the Soviet government.