What evidence supports the idea that the German blitzkrieg was successful?

Conquered Poland, Czechoslovakia, Norway and France in a very short amount of time with a lot of casualties.

In the first phase of World War II in Europe, Germany sought to avoid a long war. The German strategy was to defeat their opponents in a series of short campaigns. Germany quickly invaded much of Europe and was victorious for more than two years due to a new military tactic called Blitzkrieg (lightning war). The Blitzkrieg tactic required concentration of offensive weapons (such as tanks, aircraft, and artillery) on a narrow front.