Russians react nervously to any narrative about World War II that differs from their own. When the United States, Britain or France pay tribute to their countrymen who fought and defeated Adolf Hitler, it is seen in Moscow as an attempt to diminish Russia’s contribution. Russians hold it as self-evident that they bore the brunt of Hitler’s fury and did the lion’s share of fighting with only minimal support from the Allies.

It is a remarkably ungenerous attitude. On the 70th anniversary of the Soviet Union’s entry into the war, Russians should acknowledge the contribution of its allies. Britain in particular can — and rightly does — claim a very special...