As in World War I, Germany's main downfall was its lack of adequate allies and an attack on several fronts. Territorially, Hitler came remarkably close in World War II to achieving his quest for Lebensraum, yet his failure to concentrate his resources proved disastrous. His lack of time spent organizing the conquered territories resulted in widespread rebellions, which in turn, separated German forces. In addition, the North African campaign absorbed troops that were much needed on the Russian front. The failure of the V2 rocket in the final stages hindered the German offensives. The Allies combination of well-organized troops, weaponry, resources and a little luck in the closing stages of the war placed pressure on the already weakening Germany. Despite the early successes from Poland to France, the Battle of Britain and the invasion of Russia assured that there would be a war against the world; A war almost impossible to win.
German preparation began well before the eve of war in 1939 with the invasion of Poland. When Hitler came to power in 1933 he was able to build, at first secretly: an army, navy, and air force, despite the treaty of Versailles disallowing Germany to maintain a proper army. By this time he had built an extraordinarily powerful war machine. Despite threats from the west, the reoccupation of the Rhineland in 1936, the annexation of Austria, Bohemis-Moravia, Memel in 1938 and 1939 happened without retaliation. The British, after declaring war on Germany on September 1st 1939 did little to assist Poland who surrendered three weeks later. This helped to convince Hitler he was immune to global reaction. With the temporally secured threat from Russia on hold, Nazi forces in 1940 occupied Denmark and attacked Norwegian ports, securing iron ore imports from Sweden, which were essential for Germany's war effort.
Using overwhelming Blitzkrieg tactics or 'lightning war'; Germany's goal was to quickly defeat and occupy a nation before relief from the...