The reason Mogadishu was described as the "White Pearl" is because of its history as a beach resort for Italians and other Europeans, with luxury hotels on beautiful beaches. The origins of "White Pearl" term can be traced back to 1892 when Ali Bin Said, the fourth caliphate of Zanzibar, leased Mogadishu to the Italians.
The Italians recently started controlling most of Italian Somaliland (modern day South Somalia). 15 years later the Italians took Mogadishu outright and made it the capital of newly-established Italian Somaliland. By the 1930s the Italians developed Mogadishu, creating factories, building new buildings, railways, and roads, allowing for thousands of Italians colonists to flock to this new, modern city built along the beautiful coast of the Indian Ocean. From there beach resorts were built and Italians, and later other wealthy western Europeans traveled there for holidays. From 1936 to 1949 there was a war time lapse in Mogadishu's popularity as a tourist spot, but from 1949-1960 when the Italians regained control of Mogadishu is flourished as a beach resort for everyone from Italian Prime Ministers to British honeymooners would visit Mogadishu for a relaxing beach weekend. Post Independence in 1960, Mogadishu's status as "White Pearl" waned, but Mogadishu remained a popular beach resort into the early 70s when the Communist government took power, and tourism didn't fully stop until the late 1980s when Somalia fell into complete chaos.