How would this situation have changed the world?

What would have happened in 1989 if the Soviet Union had decided to drop a nuclear bomb on Afghanistan after their failed attempts to overtake the country through military force from 1980-1989 which cost 1 million people their lives and left millions more homeless and in desperation. The battle also led to a major civil war which eventually led to the rise of the Taliban who were seen originally as a group who would restore peace to Afghanistan.