It was the largest empire that ever existed – a vast streak of imperial pink across every inhabited continent. It was the empire on which the sun never set, covered a quarter of the world’s total land area and was home to a fifth of the world’s population. But when was the British Empire at its biggest?
The map below shows all of the areas that were at one time part of the British Empire. The empire was not, however, a solid, stable entity – throughout its history it lost territory (from the American War of Independence to the winds of change and independence movements of the 50s and 60s) and gained new lands (by conquest, treaty, discovery and mandate).
So, to answer the question, you need to examine the ever changing constituent lands of this amorphous entity. The quick answer is that the British Empire was at its largest between 1919 and 1922.
This was due to the peace terms imposed on the defeated nations in the First World War. In 1919 Britain was granted mandates over vast swathes of the imperial territory of the Ottoman and German Empires.
Under the terms of the Treaty of Versailles, Britain absorbed 1,800,000 square miles and an additional 13 million subjects. Palestine, Jordan, Iraq, Cameroon, Togo and Tanganyika all came under her direct rule. Other areas in Africa and the Pacific were granted to the British Dominions of South Africa, Australia and New Zealand.
By this point, the British Empire had reached its largest territorial extent and covered 13,012,000 square miles. Approximately 460 million people lived in its dominions, overseas territories, crown colonies, protectorates and mandates.
In 1922, the Irish Free State was created following the signing of the Anglo-Irish Treaty. At this point, Ireland remained nominally and de jure a dominion within the British Empire. In reality, it was an independent state – a position confirmed under its new constitution enacted in 1937. Arguably, then, Ireland was still included in the Empire’s land mass until 1937.
Of greater consequence for calculating the total land mass of the Empire was the withdrawal of Egypt from British proctorship. In 1922, Egypt was granted formal independence and, although Britain remained heavily involved in the country until the 1950s, it was no longer part of the British Empire.
The Empire would contract steadily in the 1930s – Iraq secured independence in 1932 and Ireland was formally removed from the Empire in 1937. This decline would accelerate both during the Second World War and in its aftermath. During the war, territories fell to Germany, Italy and Japan. After the war, decolonisation and independence would deliver final and swift death blows to the Empire.
What remains is 667,018 square miles of British Overseas Territories (of which 660,000 square miles constitutes the disputed British Antarctic claim) with 260,000 people. The formal bonds of empire were replaced (for the majority of countries) with membership of the Commonwealth of Nations.