Mongol Empire - > 40 million km2

❤️🐺 Mongol Empire - > 40 million km2 🐺❤️
💧British Empire - 33.6 million km2
🔥Alexander's Empire - 5.2 million km2
🔻Roman Empire - 5 million km2
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🔴 According to the Encyclopædia Britannica, the British Empire was the largest empire in history ever with the total area of 33.6 million km2 (including whole Australia and Canada), Mongol Empire was the second largest with 33 million km2 (without Siberia) - They count the entire Australia and Canada part of British Empire, and wittily removed Siberia from the Mongol Empire.
At the peak of British Empire, northern/western Canada, central Australia and most of areas in Africa were empty lands, if we count them part of British Empire, we must count Siberia part of Mongol Empire. Mongol Empire ruled from Korea to Hungary at it's peak, conquered over half of Europe (around 5 million km2) and threatening the other half. The total area of Asia is 44 million km2, minus Arabian Peninsula, India, Indo-China Peninsula, southeast Asia and Japan (around 9 million km2 altogether).

Therefore, the size of Mongol Empire = 44 + 5 - 9 = 40 million km2.

Japan + Southeast Asia < 3 million km2, so the total area of Mongol Empire > 40 million km2. Moreover, Mongols ruled India from 16th till 19th century with the area 5 million km2, the total area under Mongols rule > 45 million km2, way larger than the British Empire.