The largest territory by nation

Korea - Balhae(800,000km2)
China - Qing(13,150,000km2)
Russia - Russian Empire(22,800,000km2)
Mongolia - Mongol Empire(31,000,000km2)
USA - USA(10,600,000km2)
Iran - Achaemenid Empire(5,500,000km2)
Turkey - Ottoman Empire(5,200,000km2)
UK - British Empire(35,500,000km2)