Answer:
MONGOLS
Explanation:
Founded: 1206
1227 (Genghis Khan's death): 12,000,000 km2 (4,600,000 sq mi)
1206 (unification of Mongolia): 4,000,000 km2 (1,500,000 sq mi)
1294 (Kublai's death): 23,500,000 km2 (9,100,000 sq mi)
1309 (last formal reunification): 24,000,000 km2 (9,300,000 sq mi)
