On June 15,1866, Field Marshal Helmuth von Moltke, chief of the Prussian General Staff, ordered three armies - about 278,000 men - to commence operations against Austria. For more than a century, the two powers had been rivals for supremacy in the German states, and with the appointment of Otto von Bismarck as minister-president of Prussia in 1862, it soon became evident that Germany could be united under Prussian leadership only if Austria were excluded. The two had been allies in the brief and successful war against Denmark in 1864, but Prussian demands for supremacy in northern Germany made war inevitable. “It was a struggle long foreseen and amply prepared for,” Moltke admitted, “recognized as a necessity by the cabinet... for an ideal end - the establishment of power.”

Prussia's success owed itself to several factors, including good prewar planning by the General Staff in creating a superior military machine that could be mobilized quickly, the maximum utilization of railroads and the electric telegraph in both mobilization and operations, and a superior infantry weapon, the needle-gun, which could be loaded faster than the Austrian muzzle-loader and in a prone position. Moving through narrow mountain passes into Bohemia in three widely separated columns, the Prussians closed in against the Austrian position at Koniggratz on July 3 to win “the greatest battle of encirclement” in modern history. At a cost of about 10,000 men, they had soundly trounced a respected army of equal size and inflicted losses of some 44,000 casualties, nearly half of them prisoners.