In July 1870, a diplomatic dispute arose over the candidacy of Prince Leopold of Hohenzollern-Sigmaringen for the vacant Spanish throne. Fearing encirclement, France demanded that King Wilhelm I of Prussia guarantee that no Hohenzollern would ever seek the Spanish crown again. Wilhelm, vacationing at the spa town of Bad Ems, politely refused French Ambassador Vincent Benedetti's demands in an informal encounter on a promenade.
The king sent an account of the interaction via telegram to his chancellor, Otto von Bismarck. Bismarck, eager to provoke France into declaring war to rally the southern German states into a unified German Empire, saw an unprecedented opportunity. He condensed and edited Wilhelm's telegram, altering its tone to make it sound as though the King had abruptly insulted the French ambassador, and that the ambassador had breached royal protocol.
Bismarck released this doctored text to the press on July 13, Bastille Day's eve. Outrage swept through Paris. Feeling insulted, the French government declared war on Prussia six days later.
Bismarck's strategic editing achieved its intended goal: France appeared as the aggressor, causing the southern German states to join Prussia in defense. The Franco-Prussian War ended in a decisive Prussian victory, leading directly to the proclamation of the German Empire in 1871.