The saying "The sun never sets on the British Empire" means that the British Empire was once so expansive that there was always some part of it that was sunny. Though the same thing had been said of many previous empires, it was perhaps most true for the British Empire. At its greatest extent, this empire had extensive holdings in Africa, Asia, Europe and the Americas.
After World War I, when Great Britain's government took over many colonies from the losing Central Powers, the British Empire achieved its greatest extent, covering Canada, much of the Caribbean, the Indian subcontinent, Burma, Australia, New Zealand, much of eastern and southern Africa, Egypt, Sudan and parts of the Arabian Peninsula and West Africa, as well as various islands scattered across the oceans. Historians say that roughly 25 percent of the world's landmasses were under British control. Thus, the idea that the sun never set was true, in a way: some part of the Empire was always experiencing daylight. However, the saying also had a more figurative meaning: the idea that the British Empire was an eternal system, that it would never suffer decline. This aspect of the saying was not true: within a few years of 1919, Egypt and Ireland were independent, and by the 1970s almost all of the once-massive empire had formed independent nations.