Between June 1941 and May 1945, the Soviet Union and Nazi Germany fought the largest, most lethal land war in human history. Twenty-seven million Soviet citizens died — roughly one in seven. Five million German soldiers died, mostly here. The Eastern Front killed more people than the Western Front, the Pacific War, and the entire previous history of organized human warfare, combined. The Allied victory in WWII was overwhelmingly a Soviet military victory, made possible by Anglo-American Lend-Lease material and the diversion of the Western Front, but executed primarily by the Red Army — a fact the Western popular memory of D-Day and the Battle of the Bulge persistently underweights.
The German invasion (Operation Barbarossa, 22 June 1941) was the largest military operation in history — three million troops, three thousand panzers, three thousand aircraft, on a thousand-mile front. It was also the clearest expression of the Nazi ideological project: a war of annihilation against Slavic peoples and Jews, fought with explicit orders — the Commissar Order, the Hunger Plan — to disregard the laws of war and starve the conquered to clear Lebensraum for German settlement. The initial advance was staggering, encircling whole Soviet armies and reaching the gates of Moscow by December, but the Wehrmacht had gambled on a six-week campaign and had no answer to Soviet space, mud, winter, and the relocation of war industry beyond the Urals. Soviet civilian and POW losses to deliberate German policy ran to perhaps fifteen million; more than three million Red Army prisoners were left to die in German camps. The war turned at Stalingrad (winter 1942–43, where the encircled Sixth Army surrendered with over ninety thousand men), broke open at Kursk (summer 1943, the largest tank battle ever, after which Germany never again held the strategic initiative), and ended in Berlin (May 1945), with the Soviet flag over the Reichstag. The Holocaust was largely executed on this front — Auschwitz and the other death camps were in occupied Poland, not Germany, and the Einsatzgruppen shot well over a million Jews in the occupied east before the gas chambers — and the Soviet armies were the ones who liberated the camps in 1944–45.
The Russian state's contemporary self-image is built on Victory in the Great Patriotic War — May 9 is the most important national holiday, the war is invoked in every major speech, and Putin's framing of the war in Ukraine as denazification explicitly draws on the 1941–45 narrative even as it inverts who is doing the conquering. Understanding why the war is so central to Russian identity, and why the Soviet sacrifice was so extreme, is essential for reading contemporary Russian foreign policy. The scale of that loss — nearly every family touched — is also why most Russians' threshold for accepting casualties in subsequent wars has been much higher than Western strategists tend to assume.