In 1848 the Frankfurt Assembly was held, which created a single unified nation-state. A disagreement between the radical and moderate liberals of Germany arose, and the German Confederation was reinstated.
Told you! Now let's make a constitution!
10 years after the reinstatement of the German Confederation, King Wilhelm I died, and one year later, Bismarck was appointed Prime Minister of Prussia. Bismarck wanted a strong German Empire based not on liberal ideals, but on the use of military force.
Since most of the German states supported Austria during the preceding war, Bismarck needed to create a conflict to unify all of Germany. Bismarck stirred up nationalistic feelings and the forces of the Northern states, Southern states, and Prussia defeated France. They took important land, and punished them with the Treaty of Frankfurt.
The victory in the Franco-Prussian war gained the support of the German people and Bismarck could finally unify all of Germany. The constitution of the new German State was mostly the same as the Northern German Confederation, with a few minor changes.