Why was the traditional doctrine of the balance of power in post-war Europe deemed untenable?

This is due to the fact that the zone of distribution of Soviet influence was constantly expanding. Thus, Churchill, in his speech, raised concerns about future relations with the USSR. This also became the reason for the further aggravation of relations between the West and the Soviet Union. Beginning in 1946, the Cold War was unleashed between the parties, the peak of which can be attributed to the period of the Korean War, when the American and Soviet armies first clashed with each other.