The war lasted for around 38 and 45 minutes, making it the Shortest War in history. It was fought between the United Kingdom and the Zanzibar Sultanate on 27 August 1896, after the death of the pro-British Sultan Hamad bin Thuwaini on 25 August 1896 and the subsequent succession of Sultan Khalid bin Barghash.
The British authorities preferred Hamud bin Muhammed, who was more favourable to British interests, as sultan. This caused the British to invade the palace of Khalid who on turn barricaded himself inside his palace with his soldiers after refusing to step down. The end of the war saw the victory of the British side.

Read more
https://en.m.wikipedia.org/wiki/Anglo-Zanzibar_War