What event is considered the end of the cold war and why?

The falling of the Berlin War ended the cold war.

Explanation:

The Berlin War was a symbol of communism that was majorly the propaganda of the cold war. The fall of the Berlin War led to opening of borders and the free elections held ousted the Communist party which meant an end of Communism.

This therefore was the end of the cold war. In 1991, when the Soviet Union dissolved into component elements, the big power ceased to exist and therefore ended the cold war and also the dominance of the Soviet Union.