Otto von Bismarck was the mastermind who united all of Germany. Known as the Iron Chancellor, he served during the reigns of Emperors William I and Frederick III. In 1864 Prussia and Austria occupied the Danish provinces of Schleswig and Holstein; after Bismarck maneuvered Austria into the Seven Weeks' War in 1866, Prussia annexed the two provinces, as well as Hanover and other north German states. Bismarck reorganized Germany and excluded Austria. The states north of the Main River united with Prussia in 1867 in the North German Confederation.