What internal and external forces shaped the story of self-government in the two Germanys, and then the reunification of Germany?
Another part of the appeal of the Nazi party was the play to the common worker's nationalistic pride in Germany and the hope that the Nazis presented of Germany arising to greatness again after the defeat of World War I. Hitler was very effective in playing to the emotions of a populace that was searching for a restoration of national dignity. After World War II, the defeated and disheartened Germans weren't allowed or able to consider reunification for many years.
Another force was industrial capitalism, which fueled many of the class antagonisms that nationalists like Otto von Bismarck tried to dismantle or sublimate into other directions. Germany became a world power very quickly after unification largely through its industrial might. Bismarck was able to assuage many of the issues faced by German workers through social security programs that actually tied them to the state and increased their loyalty.
On the other hand, reunification was delayed by the wishes of both the Soviet Union and the United States, who held sway over Germany in the wake of World War II. Over time, however, West Germany's rebirth as an economic power helped to facilitate reunification by providing a solid base for integration. It also provided a contrast for many Germans and other Europeans with the austere, struggling economy of East Germany, where the average standard of living was much lower.
This is a pretty big question in that it covers a great deal of time. The major factor that shaped self-government in Germany was the conservatism of the aristocracy. It prevented the development of a democratic Germany, which helped to bring about Nazism, WWII, and the eventual splitting of Germany.