By the year 300, the initial period of Germanic invasions into the regions held by the Roman Empire had come to a close despite sporadic unrest as noted in the particular cases presented above. Although the Goths had, just thirty years before, split into the Ostragoths and Visigoths, they were settled somewhat peaceably in Dacia. The Vandals had moved into the region along the Danube. The Alemanni and Franks were quietly settled along the Rhine. From 300 AD onward, in addition to armed incursions, a more successful form of invasion was launched by the Germanic tribes on their Roman neighbors: invasion by colonization.
From as far back as 12 BC, when Roman armies traveled by boat via the North Sea and subdued the Frisians and Saxons, the Germanic people who were captured in a confrontation were taken into the Roman Empire as colonists rather than as slaves. The Roman emperors apparently believed that if the captured tribes would be allowed to maintain their lifestyle they would benefit the Empire. It was more advantageous to have a happy colonist than a disgruntled slave. For the most part, the Germanic people who were absorbed into the Roman Empire in this manner did indeed cooperate with their Roman overlords. They preserved their native customs and beliefs. The village communities they established retained all the trappings of Germanic culture despite being in close proximity to Roman communities.
According to James W. Thompson, in his book History Of The Middle Ages, "Thousands of Goths were so colonized by Claudius II, thousands of Franks and Alemanni by Aurelian, thousands of Bastarnae and Franks by Probus, thousands of Carpi by Diocletian, thousands of Chamavi and Frisians by Constantius".
By the Third Century, the majority of Germanic colonists in Roman territories were not captured antagonists, but rather voluntary Germanic refugees. Germanic men enlisted into the Roman Legion in large numbers when they found that, unlike the Germanic tribal army, the Roman army would actually pay them for their service and give them daily rations of food. In some cases, a chieftain would enter into an alliance, or foederati, with the Roman army, and with him would go the entire tribal army. Another situation existed in which a Germanic family would receive a certain tract of land to farm, on the condition that the male head of the family be willing and ready to go into the army when summoned. These military colonists, or laeti, were often located in the border regions. The Roman Empire was confident of its power, and felt no qualms at admitting the Germans into positions of leadership. It is interesting to note that in the year 380, the Roman legions in Gaul were under the command of a Frankish leader.
The period of 375 to 568 has come to be known as the "period of the barbarian invasions". During that time, the number of Germanic people who were migrating into the Roman Empire and the effectiveness of those migrations in bringing about the destruction of the Empire increased dramatically. The renewed invasions of the Germanic tribes into southern Europe has been likened to a great wave sweeping over the land, washing everything away in its path.
The Alemanni pushed into the region lying between the Rhine and the Danube Rivers known as the Agri Decumates, or Tithe Lands. The Tithe Lands had been set aside by the Roman emperors for retired veterans of the Legion. A wall was constructed which ran from Regensburh to Mainz to protect the region from invaders, but it did not keep the Alemanni out. A line of castles was established along the upper Rhine, but they were not very effective.
The Visigoths moved into the Balkan Peninsula and scored a victory at Adrianople over the Roman Emperor Valens in 378. They settled somewhat peacefully along the middle and lower Danube until the year 408 when they invaded Italy. Rome was sacked by the Visigoths in 410 AD. Then, two years later, they moved westward into Gaul and Spain.
The Vandals invaded Gaul in 406 where they engaged in warfare with the Franks. By 409 AD they were settled on the western side of the Pyrenees as foederati of the Roman Empire. The Vandals were not destined for peace in Gaul. The Roman Emperor encouraged the Visigoth tribe led by the chieftan, Wallia, to attack the Vandals and the Alans and Swabians, two other Germanic tribes that had entered Gaul. The Vandals crossed the Straits of Gibraltar in 429 and captured most of the Roman Empire's strongholds in northern Africa. They would, in 455, capture and sack Rome, but then in 533 Emperor Justinian would destroy the Vandal kingdom established in northern Africa.
Other Germanic tribes moved en masse into the western portion of the Roman Empire. The Burgundian tribe moved into the valley of the upper Rhine about 443. They eventually took control of the region stretching from Lake Geneva to Provence. The Franks, who thrived in settlements in northern Gaul, practically smothered out any remaining vestiges of the Roman Empire by the year 486. The alpine regions of modern-day Alsace and Switzerland constituted the primary residence of the Alemanni throughout this period. The Bavarians settled in along the Danube River. The Lombards migrated around the Alps to settle the Po Valley of Italy.
While the migrations of the Germanic tribes were primarily southward toward the Mediterranean, the Jutes, Angles and Saxons headed west to invade the British Isles.
Over the course of the next two or three centuries, the various tribal territories of Germanic peoples took on the aspect of kingdoms. Particular individuals or families began to assert themselves within the tribe and the concept of "kingship" was embraced by those individuals or families.