Let us therefore brace ourselves to our duties, and so bear ourselves that, if the British Empire and Commonwealth last for a thousand years, men will still say, "This was their finest hour". World War II was the single most destructive war in history, claiming over 60,000,000 lives and untold material damage. In contrast to 1914, most soldiers in 1939 had a better sense of the seriousness of modern war and marched off with grim resolve rather than enthusiasm. The war in Europe can be seen as happening in two phases: the German blitzkrieg (1939-41) and the allied response and counterattack (1942-45). Technological and tactical innovations were central to each phase and affected events on both the Eastern and Western fronts. As in World War I, many generals at the start of World War II were planning to fight the last war rather than the next, hardly taking into account the changes in warfare over the last twenty years. France, in particular, operated with a World War I siege mentality, relying on a giant enclosed concrete trench, the Maginot Line, which covered much, but not all, of its border with Germany. However, the German generals had a very different perspective. Having lost the last war, they were more determined to find a new way to win the next one. In their minds, that way was blitzkrieg (lightning war). Blitzkrieg was largely the brainchild of Heinz Guderian, a German tank expert who convinced Hitler that the future of warfare lay with tanks and airplanes, not immobile lines of trenches. Instead of spreading tanks along the front as infantry support, Guderian's idea was to amass his panzer (tank) divisions at strategic points and blast through that part of the line. The German airforce, the Luftwaffe, would bomb and strafe the enemy behind their lines, further demoralizing and disrupting them. Meanwhile, infantry would consolidate their hold on the gaps blown open by the panzers. This would force the enemy back to a new position that was already weakened and threatened by the panzers and Luftwaffe wreaking havoc in their rear. Blitzkrieg did not do away with the continuous front, since the manpower and firepower needed to fill a continuous front were more available than ever. What it did accomplish was to make the continuous front mobile, thereby pulverizing everything in its path. As a result, the fighting was not confined to a narrow static front, as in World War I. Rather, it swept across all of Europe in a broad swathe of destruction. Also, Blitzkrieg was designed for attaining short decisive victories that would avoid the prolonged type of warfare that had worn Germany out in World War I. At first it took its enemies by surprise and allowed the Nazis to overrun their enemies in both Eastern and Western Europe very quickly. In the East, the German blitzkrieg easily overran western Poland while Stalin took the rest. Then, while Hitler was pre-occupied with defeating France and Britain in the west, Stalin invaded Finland and took the Baltic republics of Latvia, Estonia, and Lithuania (lost since World War I) as well as part of Romania. These events, along with Hitler's long-standing hatred of Russia, prompted a planned invasion of Russia, which was delayed by having to help Mussolini in the Balkans and North Africa. When it did get going in June 1941, the German attack met with incredible success, quickly inflicting tremendous casualties and driving almost to the gates of Moscow. Only the onset of winter temporarily stopped the German advance and bought the Russians time to recover. In the West, Hitler also met with startling success as the German army rapidly overran Denmark, Norway, Belgium, Holland and France by June 1940. Not until they reached the English Channel did the Nazi advance halt and give Britain renewed life. The ensuing Battle of Britain was the first major battle ever decided primarily by air power, as the Luftwaffe first bombed British airfields and then concentrated on Britain's cities to clear the way for an invasion of Britain. However, the British grimly held on until Hitler abruptly broke off the raids to turn his attention to the invasion of Russia.