The German people also have experienced a variety of political institutions—rule by emperors, kings, and princes, representative institutions and republics. In studying German history one can benefit from understanding the relationship between geography and the growth of military institutions. Germany has often been contrasted to Britain, which has been protected by the water, while Germany has lacked frontiers and required a strong military to defend it from potential enemies on all sides. Germany also was internally weak, even though it encompassed the Holy Roman Empire, which began with the Saxon, Otto I, who was crowned king in 962. By the end of the Middle Ages there were, however, some 300 states—duchies, counties, ecclesiastical territories, free cities, and other territories. There was no clear boundary to the west, where the German states were threatened by the French king, or to the east, where Slavic tribes predominated. During this period the Germans themselves colonized the east in one of the greatest movements of peoples before the American West was settled. Here the Germans settled in areas associated with the names of Mecklenburg, Pomerania, and Brandenburg, and they pushed into Silesia. This eastward expansion indicated a new direction of German influence, with which the Hohenzollern family, which created Prussia, was associated.
Many cleavages have divided German society throughout history. Ethnically, the Germans were not homogeneous. The religious conflicts between Protestants and Catholics during the Reformation created other serious divisions. Some historians even claim that Germany was never thoroughly Christianized, and its pagan tradition erupted again during the Nazi regime. Other divisions existed in the political and cultural realm and among the social classes. Political disunity, however, was the most obvious division.
The Germans oscillated between universal empire and localism. When nationalism belatedly developed, attempting to bridge these differences, it ended up becoming a most violent kind. The 18th century saw the rise of the state of Prussia and the violent threat of the French Revolution and Napoleonic Wars, which revealed the weaknesses of Germany but led to a widespread growth of national feeling. Unfortunately, the Congress of Vienna militated against the growth of unity. The rivalry between Prussia and Austria prevented the growth of a true federation that might have led to a unified state. The revolutions of 1848 were a turning point for Germany, during which the Germans failed to turn toward democratic government and create a successful unified state based on a liberal constitution. In the end it was the authoritarian Prussian Junker, Otto von Bismarck, who set himself the task of destroying liberalism in order to strengthen conservative Prussia and maintain its position as a great power. Prussia and Prussianism eventually triumphed over the rest of Germany, which was more passive, liberal, and good-natured. Bismarck and Prussia impressed on the Germans a spirit of militarism and the Machiavellian doctrine of the reason of state, which justified every infringement of written and unwritten law. These were qualities that found even greater expression in the leadership of Adolf Hitler. The cleavages continued after World War II, as West and East Germany were divided between a democratic Federal Republic and a communist German Democratic Republic. Today the Germans are still trying to bridge those differences since they were reunified in 1990.