Roots of war
On 22 June 1941, some three million soldiers of Germany and her allies began an attack on the Soviet Union. This war was supposed to be over in a matter of months, but it lasted for four years, and grew into the largest and most costly conflict in all history.
It was here, in the vast struggle between the two dictatorships, that the German army was defeated and the outcome of World War Two was decided in favour of the Allied powers - the British Empire, the United States and the USSR. The cost to the Soviet Union was an estimated 27 million dead.
The roots of the war lie in the appointment of Adolf Hitler as German chancellor in 1933. His hatred of Soviet Communism and his crude ideas of economic imperialism, expressed in the pursuit of Lebensraum ('living-space'), made the Soviet Union a natural area for Hitler's warlike ambitions.
After the outbreak of war in 1939 came the added fear of Soviet expansion in Eastern Europe, while Germany was fighting the British Empire and France in the west. All of these factors contributed to the decision taken by Hitler in July 1940, after the German defeat of France, to plan for an all-out assault on the Soviet Union.
Not until December 1940, however, did Hitler make a final decision to go ahead with what became known as Operation Barbarossa. The original date, set for May 1941, had to be revised to complete the vast preparations for the attack - following other German attacks on Yugoslavia and Greece in April.
The date of 22 June was late for starting a campaign over such a vast area, but German commanders were confident that the Soviet armed forces were primitive, and that the Soviet people were waiting for liberation. Victory was expected by the early autumn.
Battle of Stalingrad, 1942
The attack came as a complete surprise to the leader of the Soviet Union, Joseph Stalin. Despite repeated intelligence warnings, which included the precise day and hour of Germany's incipient assault, Stalin remained convinced that Hitler would not risk an eastern war as long as the British Empire remained undefeated. It has been argued that Stalin in fact planned a pre-emptive attack on Germany for the early summer of 1941, and was then thrown off-balance by the German invasion.
The evidence makes clear the defensive posture of the Soviet Union in 1941. Stalin did not want to risk war, though he hoped to profit from the German-British struggle if he could. In the event, the shock of attack almost unhinged the Soviet state, and by the autumn German forces had destroyed most of the Red Army and the Russian air force, surrounded and besieged Leningrad - where over one million people died of starvation and cold - and were approaching the outskirts of Moscow.
The Red Army had sufficient reserves to stop the German army from completing the rout in December 1941, but the following summer German offensives launched far to the south of Moscow, to seize the rich oilfields of the Caucasus and to cut the Volga shipping route, created further chaos.
Hitler hoped that German forces would capture the oil and sweep on through the Middle East to meet up with Axis forces in Egypt. The Volga was to be blocked at Stalingrad, after which German forces could wheel northwards to outflank Moscow and the Soviet line.
The southern attack failed at Stalingrad. After weeks of chaotic retreats and easy German victories, the Red Army solidified its defence and against all the odds clung on to the battered city. In November 1942 Operation Uranus was launched by the Soviets, and the German Sixth Army at Stalingrad was encircled.
Some historians have seen this as the turning point of the war. But not until the Red Army had decisively defeated German forces in the more favourable summer weather of 1943 did the tide really turn.
The Battle of Kursk in July 1943 was one of the greatest set-piece battles in military history. The Red Army withstood a massive German assault, and then counter-attacked. For two years Soviet forces pushed the German army back into Germany, until in May 1945 Soviet forces accepted the surrender of the relic of Hitler's army in Berlin.
The central question of the German-Soviet war is why, after two years of defeats, and the loss of more than five million men and two-thirds of the industrial capacity of the country, the Red Army was able to blunt, then drive back, the German attack.
The idea that the USSR had limitless manpower, despite its heavy losses, is inadequate as an answer. Germany and her allies also possessed a large population, and added to it the peoples of the captured Soviet areas - men and women who were forced to work for the German army or were shipped back to work in the Reich. Soviet armies were always desperately short of men.
Above all, Soviet tactics in 1941-2 were extremely wasteful of manpower. If the Red Army had continued to fight the same way, it would simply have sustained escalating losses for little gain.
Nor did the USSR enjoy an advantage in economic resources. After the German attack, Soviet steel production fell to eight million tons in 1942, while German production was 28 million tons. In the same year, Soviet coal output was 75 million tons, while German output was 317 million. The USSR nevertheless out-produced Germany in the quantity (though seldom in the quality) of most major weapons, from this much smaller industrial base.
The impressive production of weapons was achieved by turning the whole of the remaining Soviet area into what Stalin called 'a single armed camp', focusing all efforts on military production and extorting maximum labour from a workforce whose only guarantee of food was to turn up at the factory and work the arduous 12-hour shifts. Without Lend-Lease aid, however, from the United States and Britain, both of whom supplied a high proportion of food and raw materials for the Soviet war effort, the high output of weapons would still not have been possible.
The chief explanation lies not in resources, which Germany was more generously supplied with than the Soviet Union, during the two central years of the war before American and British economic power was fully exerted. It lies instead in the remarkable reform of the Red Army and the Russian air force, undertaken slowly in 1942.
Every area of Soviet military life was examined and changes introduced. The army established the equivalent of the heavily armoured German Panzer divisions, and tank units were better organised - thanks to the introduction of radios. Soviet army tactics and intelligence-gathering were also overhauled.
Camouflage, surprise and misinformation were brilliantly exploited to keep the German army in the dark about major Soviet intentions. The air force was subjected to effective central control and improved communications, so that it could support the Soviet army in the same way as the Luftwaffe backed up German forces.