Though France was already at war with Nazi Germany by the time the Germans invaded in 1940, it was not militarily necessary for the Germans to invade. However, Hitler felt that he needed to invade France for sound strategic and political reasons.

The Nazi dictator believed that it was necessary to neutralize the main Western European powers—Britain and France—and keep them out of the war. This would allow him to turn his attention towards his most important goal: the establishment of a racial empire in Eastern Europe.

Hitler knew that he had to complete the invasion of France quickly in order to achieve the maximum effect. The quicker the German victory, the more likely it would be that the will to fight among the Western powers would be broken. However, that didn't happen. The lightning-quick defeat of France and the Low Countries in just six weeks simply made the British under Churchill all the more determined to resist the Nazi threat, even if it meant standing alone.

The last thing Hitler wanted was to have to fight a war on two fronts. To that end, he hoped to ensure that Western Europe would be pacified before Germany turned its attention towards the East. And although the defeat of France and the Low Countries in double-quick time went some way towards achieving this aim, the stubborn resolve of the British made it more difficult to carry out his plans.