Tanks and different armoured vehicles.

Because Allied soldiers and armoured vehicles could finally challenge the German armies face to face.

During World War II, Germany suffered substantial losses to its aircraft. An estimated 76,875 German airplanes were destroyed in the fighting.

world war 2

EDIT (Rigel of Orion): World War II, but if you want to be literal, you could include World War I. Hitler was a soldier fighting in the German Military in World War I.

In World War I it was the assassination of the heir to Austrian throne, in World War II it was the German invasion of Poland even though Japan had been fighting China two years before that.