The territory of each country is changing through times. Each state in the world has reached its territorial peak, which then ends.
The British Empire had 35.5 million square kilometers under her rule and is the biggest empire ever built. Today Great Britain has a little 0.21 million square kilometers which brings the ratio between the largest extent and current territory to 0.59 percent. That means that the British lost 99.41 percent of their holdings. Mongols lost 93.6% of their territory, and Spaniards – 96.7%.
Also, large territories have lost Turkey (Ottoman Empire), Armenia, and Brunei.
The Danes controlled Norway, Sweden, Filnaln, Iceland, Wessex, in southern England.
The Czechs controlled Austria, Slovakia Poland, and Hungar.
The Hungarians ruled Slovakia, Romania, Serbia, Slovenia, Croatia, Macedonia, Montenegro, Bosnia and Herzegovina.
Poles controlled the Czech Republic, Slovakia, Ukraine, and Belarus.
The United Kingdom
The British Empire was the largest empire in the history of mankind by the total size (35.5 million km2 or 13.71 million mi2 [26.4% of the world]).