That is not precisely what I am saying.
Reagan certainly did not act alone everything he did could have been undone by the Soviets of earlier years, before the years of disillusionment had eroded the faith of the Soviet man.
Reagan certainly did not act alone if there had not been previous presidents that weakened and bled the USSR with words and deeds secret and public the Soviets might not have been so demoralized and weak. President Carter as a standout example.
The leaders of other Nations and the Catholic church also took effective actions and multitudes of individuals learned and acted Matthias Rust being an unusual example flying into the USSR while many thousands voted with their feet trying to get out.
So I can't maintain that Reagan alone ended the Soviet Union, but he was a big part of the leadership and direction that brought a long festering corruption to the point it could erupt, And because the people within the Iron Curtain were so ready for it that they lanced the boil from within , this happened without the millions of casualties that had been so long predicted.
So Reagan was not alone , perhaps not even indispensable , but Reagan led when many were too timid Reagan led.