Zanzibar, an island nation that is now part of Tanzania, has been a contested territory for centuries. Starting in the 15th century, interested parties from Portugal, Oman, Germany, and Britain vied for the right to settle in Zanzibar and to decide whether to continue or abolish its slave trade.
In 1890, Zanzibar was declared a protectorate of the British Empire. And three years later, the Britain-friendly sultan Hamad bin Thuwaini came to power. Sultan Hamad died unexpectedly on 25 August 1896; his young cousin, Khalid bin Bargash, was suspected of having poisoned him. Young Khalid thumbed his nose at the British by swiftly moving into the palace without their permission, and ignoring a warning from the British consul to cease and desist. Instead, Khalid mobilized nearly 3,000 soldiers and civilians in the palace square, as well as a variety of military equipment that the British had gifted to the previous sultan.
The British, in response, readied warships in the harbor and delivered ultimatums demanding that Khalid leave the palace. Khalid remained defiant.
At 9:00am on 27 August 1896, three British ships opened fire on the palace. By 9:02am Khalid had fled, and most of his weaponry had been destroyed. The open fire ended at around 9:40am. A new (British-approved) sultan was in place by the afternoon.
Unsurprisingly, given that the British commanded the most powerful navy in the world, the war was a lopsided one. While approximately 500 Zanzibaris were killed, only a single British sailor was wounded. As the Anglo-Zanzibar War lasted between 38 and 45 minutes in total, it remains the shortest war in history.