The British expedition to Abyssinia/Ethiopia, considered to be "one of the most expensive affairs of honor in history," was a large military expedition sent by the British to rescue a bunch of missionaries and diplomats that had been taken hostage by the Ethiopian Emperor Theodoros II. It all started when Theodoros received a pair of pistols from Queen Victoria of the United Kingdom as a gift. After several embassies to the UK which fell on deaf ears, he decided to take a large number of European advisers, missionaries, and diplomats hostage. In response, the British sent General (later Field Marshal) Napier and 11,000 Indian Army troops (a mix of British and Indian troops, including a large detachment of Sikhs) to go rescue the prisoners and punish Theodoros.

British casualties in the campaign were rather hilarious: more people died from sunstroke (10) than gunshot wounds (3), and of the three gunshot wounds, one was a suicide and another was an accidental self-shooting. Ethiopian casualties were very heavy, including Theodoros, who killed himself at the end.

Source: Hozier, the British Expedition to Abyssinia