The ideas of Islam spread quickly throughout Afro-Eurasia because of migrations due to drought, the expansion of trade networks, and military conquest that brought new communities under Islamic rule. The Islamic empires beginning with the Umayyad and continuing into the Abbasids were incredibly wealthy and powerful in the Mediterranean and across southwest Asia. Wealth grew enormously because of trade, a deep quest for knowledge led to incredible innovations in medicine, mathematics, and astronomy, and Islamic tradition preserved much of the classics from Greece and Rome.