The rise of Otto von Bismarck and the unification of Germany.
Otto von Bismarck became the greatest statesman of a generation, but he began as an intransigent and irresponsible youth. He coasted through college, got himself thrown out of an early political appointment, and caused havoc with his divisive opinions during a meeting of parliament.
Bismarck was just starting to get the hang of diplomacy when the throne of Prussia passed to a new Frederick Wilhelm who promptly sent him away to Russia. But then Bismarck got tapped to serve as the Head of Government and began pushing for his great project: the unification of Germany.
Bismarck turned up the heat on his long-term plan to unite the German Confederation under Prussian leadership. He allied with Austria to seize a piece of disputed land, then maneuvered them into a war that he decisively won. Even an assassination attempt could not stop him.
The northern German states now looked to Prussia for leadership, but that power brought increased attention from their enemies. Bismarck engineered a war with France by striking at Napoleon III's pride and wound up winning a runaway victory to secure Prussia's diplomatic power.
You would think that capturing the Emperor of France would end the war, but... no. Who could Bismarck negotiate with? Eventually he forced an interim government to cave to his demands, and at the same time convinced the rest of the German states to unite with Prussia.