The Arab invasion of Roman Hispania started the better part of 1,000 years of alternating war and peace over the Iberian Peninsula. The various Arab and Ottoman Empires faced off against the surviving Christian kingdoms in the mountains that would form modern Portugal and Spain and the various Successor State Roman Empires from Charlemagne to the Holy Roman Empire that was famously mocked as neither Holy, nor Roman, nor or an Empire.

The Arabs and African Berbers moved in when they pushed the locals into the mountains, took over the existing Roman infrastructure, and built a new Islamic civilization over the ruins of the old one. They officially allowed other religions to exist of course, but their laws were clear on who was superior and who was not. What history now calls the Reconquista of Spain began when they demanded an exorbitant tax from the surviving Christians.

The Christians chose to fight rather than pay the heavy taxes, and furthermore decided if they were going to fight, they wanted all of their land back. The alternating wars and peaces that followed from the north of Spain all the way to the Mediterranean and Atlantic Coasts resulted in the eventual expulsion of millions of Muslims who refused to convert to Christianity. That made this both a mass migration INTO Hispania and then back out to Africa and Arabia a thousand years later.