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Mongol commanders sometimes spread accounts of brutal punishments inflicted on cities that resisted them. The threat of destruction could persuade other settlements to surrender without a prolonged siege. Psychological warfare complemented the Mongols' mobility and military organization, helping relatively small forces control enormous territories.

During the total solar eclipse of 1919, astronomers photographed stars appearing close to the Sun. Their apparent positions shifted because the Sun's gravity bent the light reaching Earth, as Einstein's general relativity predicted. The measurements had limitations, but their announcement became a worldwide sensation and helped establish Einstein's public reputation.