In just over one hundred years following the death of Mohammed in 632, the Arab followers of the Prophet had subjugated a territory with an east-west expanse greater than the Roman Empire, and they accomplished it in about half the time. By the mid-eighth century, Arab armies had conquered the thousand-year-old Persian Empire, reduced the Byzantine Empire to little more than a city-state based around Constantinople, and destroyed the Visigoth kingdom of Spain. The cultural and linguistic effects of this early Islamic expansion still reverberate today.
The Great Arab Conquests by Hugh Kennedy
Many conquerors have come and gone, but the Islamic conquest had a devastating impact on the world — arguably a more devastating impact than any conquest before or since, including Alexander the Great, Hannibal, and Ghengis Khan — because it wasn't merely a matter of the new conquerer gaining tribute. The Islamic conquerors took everything from the newly conquered: money, language, culture, traditions, wives, children, values. Everything. The nature of Islam is that it replaces cultures wherever it gets a foothold.