In 1806 Prussia engaged in war with Napoleon. The swiftest of his triumphs followed. In two months the Prussians had surrendered their fortresses, and seen annihilated the greatness which Europe had failed to crush in the time of Frederick the Great. A period of humiliation followed, and for some years the people lived under the conqueror's yoke.

Deliverance came when Napoleon, stretching too far his power, and arousing the spirit of peoples, was defeated by Europe in arms. The liberation which alone Prussia could not have accomplished, was yet wrought partly by herself, for deliverance was preceded by regeneration in which her military system was fundamentally reformed. But it may be that what remained after all as the principal heritage from these years was the abiding sense that Prussia had suffered from being weak, and that only through military strength could there be safety in the future.

The expansion and greatness of Prussia left unfulfilled the old idea of a united Germany. Through the middle ages and down to this time Germany had remained disunited, and weak and despised because of it. The smallest states had now disappeared, but still there were larger ones, grouped under Austria in vague and shadowy empire. And the history of Germany in the half century which followed the downfall of Napoleon is a record of yearning and striving on the part of people filled with distant memories, and noble aspiration after that strength and union which had come to their neighbors and yet been denied to themselves.