Europeans used to fight wars to keep these people invading their homelands, now they voluntarily let them in.

The Muslims invaded North Africa and the Middle East and took the land from the Romans and Byzantines (Eastern Romans) by force.
The struggling Romans asked for help from the West to fight off the Moslems and the Turks and
the Crusades were born. Something they conventiently skip out of the history lessons......the Muslims
invaded the territory of the Eastern Romans and forced the locals to convert.
Spain had also been
invaded by Muslims and had to be reclaimed by military force by Europeans.