The shortest war in history lasted about 40 minutes.
On 27 August 1896, Britain went to war with the Sultanate of Zanzibar after a sultan Britain did not approve of took the throne. British ships opened fire on the palace at 9:02 and the sultan's flag came down before 9:45.
Why is this true?
The bombardment set the palace on fire and sank the sultan's only warship. The sultan fled to the German consulate and a British-approved successor was installed the same afternoon.
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History keeps producing facts that ruin your sense of time. A war shorter than a lunch break, an empire that overlaps with the invention of the fax machine, a queen who lived closer to the Moon landing than to the pyramids. The entries here favour events with solid documentation, and each one explains the context that makes the surprise make sense rather than leaving it as a bare curiosity.