The discussion by Pohnpei397 raises some valid points regarding the effectiveness of Germany’s “blitzkrieg” strategy during the initial phase of World War II. It omits, however, some very important and very elementary points regarding Operation Barbarossa, the June 1941 invasion of the Soviet Union. No answer to a question regarding the success of that strategy can possibly be complete without reference to two main points regarding Operation Barbarossa. The first point is that, by invading the Soviet Union, Germany effectively placed itself in the position of having to fight wars on two broad fronts, to the east and to the west. A two-front war guaranteed that the German Army, the Wehrmacht, would have to divide resources between those two fronts. Any competent general, and Hitler did not lack for those, warns against opening oneself to a multi-front engagement that forces difficult decisions about allocation of men and material.
A second point omitted from the earlier answer, and the most important point, involves the timing of the launch of Operation Barbarossa. As all military historians know, the Balkans were an extremely important region for Germany. Not only were the natural resources, especially oil, primarily from Romanian oil fields, essential for the Wehrmacht’s ability to sustain an invasion of the Soviet Union, but denying that territory to the Soviet Army in itself helped protect against the opening of yet another front. Recognizing this, Hitler ordered the execution of Operation Marita, the invasion of Greece and Yugoslavia. The difficulties experienced by the Germans in pacifying the Balkans, however, had a profound impact on the success of Operation Barbarossa, delaying the start of the invasion of the Soviet Union by one month – a crucial period of time. That one month delay in the start of Barbarossa would prove of enormous consequence. As the previous answer correctly notes, the vast expanse of the Soviet Union constituted a serious obstacle for German military planners. It would not, however, have been an insurmountable obstacle but for the one month delay in launching the invasion. That month cost the Germans dearly, because it brought closer the start of the brutal Russian winter, which, again, all military historians acknowledge, played a significant role in the ultimate failure of the invasion. The German Army, its supply lines stretched across the vast Russian plains, suffered incredible difficulties when fall rains ruined the roads upon which German supply trucks and armored vehicles drove, and the severe cold and heavy snowfalls proved too much for the German troops, who, assuming a summer victory, were ill-prepared for the cold.
The invasion of the Soviet Union came very close to succeeding, at least in terms of reaching and conquering Moscow and other major population centers. Germany’s own occupation policies, however, would undermine those short-term victories. The Germans were so brutal in their tactics that they turned otherwise welcoming villages into recruiting grounds for anti-German partisans. In short, however, planning errors and that one-month delay doomed Operation Barbarossa to failure. Had the invasion been launched on time, and had German logistics been better planned and executed, the invasion could have succeeded.
I would argue that the set of tactics known as blitzkrieg were largely successful but that they were not successful in all circumstances. Blitzkrieg was a highly mobile style of war that relied heavily on supply lines. For this reason, it worked well in relatively small areas where supply lines could not become overstretched. However, when it was attempted in the huge open spaces of the Soviet Union, it was not quite able to succeed.
Germany was clearly successful in its attacks on Poland, the Low Countries, and France. Some of the credit for this success must surely be given to blitzkrieg tactics. The tactics, which were not anticipated by the armies of the countries Germany invaded, allowed the Germans to gain rapid victories. We should, however, avoid giving all of the credit to blitzkrieg. Germany had a bigger and better military than Poland or the Low Countries did. Germany could probably have defeated those countries rather easily even without using blitzkrieg. Even so, we can still say that the Germans might not have won so quickly (and might not have defeated France at all) without blitzkrieg.
Germany’s major failure in the war, and the one that ultimately led to its defeat, was its failure to defeat the Soviet Union when it invaded that country in 1941. In this instance, it appears that blitzkrieg failed. In one sense, it is hard to say that it really did fail. After all, German troops conquered large areas of Soviet territory and came close to capturing Moscow in the first few months of the Soviet campaign. This was accomplished in part by blitzkrieg. However, the sheer size of the Soviet Union’s territory and population (and its willingness to fight extremely hard) eventually defeated the Germans. The Germans were not able to get enough supplies to its armies to allow them to maintain their attacking, blitzkrieg tactics.
In short, it would appear that blitzkrieg was a successful tactic when applied in the proper strategic context. It was a tool that could be used to great effect in relatively small spaces, particularly when the opposition was not extremely strong. However, when the Germans tried it in the vast Soviet Union, it failed. We can argue, then, that blitzkrieg was a successful tool of war but that it failed when it was used in the wrong circumstances.