Kublai Khan had a diverse group of Mongols, Chinese, Central Asian Turks, Persians, Indians, Tibetans, etc in his empire. I would call that pretty diverse. The Ottomans were a diverse empire. The Romans were a diverse Empire (of Africans, Arabs, Europeans, Central Asians, etc). The Indians Empires have been very diverse. The Egyptians were diverse - they had black Nubians, Arabs, etc. 

I am not talking about how long societies last. I was talking about successful empires. During the heydey of the Arabs, say 11th century Baghdad, one would find Chinese, Indian, Arab, European and African traders and immigrants there. Many of the Arab Caliphate's greatest thinkers (Ibn Sina, who was born in Spain) were immigrants.