With a POD after August 1, 1939, have by the year 2000, neither Berlin nor Moscow be viewed as the most powerful city in Eastern Europe.
Eastern Europe for these purposes is East of Salzburg, Austria, West of the Urals and North of Belgrade.
No more than 10 times the Nuclear Tonnage of Hiroshima should be dropped in the area, and the population of the area shouldn't drop to less than 50% of the area at the same time iOTL. (So only Krakow surviving the 1985 Shanghai Flu Pandemic doesn't count)