The Cause For The Great Migrations The cause for the “Great Migrations” was to plunder new lands and settle. Germanic tribes had for centuries challenged the Roman frontiers because their primitive, unproductive economies forced them to search constantly for new lands to plunder or settle. The Germans were attracted by the wealth and splendor of the Roman world, and the Romans admitted them into the Empire, even while resisting their armies. The barbarians came initially as slaves or prisoners of war, then as free peasants to settle on deserted lands, and finally as mercenary soldiers and officers. In the fourth century the barbarian penetration of the Roman Empire was made more