The Sea Peoples that appeared out of nowhere in the Mediterranean were almost certainly a form of mass migration. Our records of that era, centuries before the birth of Christ, are fragmentary, and we don’t even know where they came from. All we know is that they showed up one day and everyone lived to regret it. The civilizations of the area had a complex trading relationship with each other, and they sent letters everywhere. The letters we’ve recovered tell the tale of a complex network of advanced kingdoms. And then one some of them fell silent. Some sent pleas for help when people arrived from the sea and overwhelmed them. They come one after another, from one end of the sea to the other. One of the most poignant letters we’ve found is a report from the Egyptian army that they won. The Sea Peoples had been defeated. And the Egyptian’s own losses were so horrible, so vast, that they didn’t know if their army or empire would survive to celebrate the victory.

The Roman conquest of that same area centuries after those great kingdoms collapsed certainly had aspects of mass migration. Roman Citizens could go anywhere they wanted, and they did so in peace after the Romans armies killed enough locals to teach them what happened if they resisted. The Muslim conquest of three-quarters of the Roman Empire was absolutely another example that could fit the definition in broad strokes. The Mongol Hordes that road from one end of Asia to the other and even brought the last remnants of Pseudo-Roman power low were another. The majority of the people in the world actually share DNA going back to those Mongolians, showing just how intimately their strong young men migrated when they came to a new land.