Two Phases of Migrations

I quote here part of a Wikipedia article making only a few modifications to it. The article gives good general outline of the difficult to study Migrations Period from Constantine the Great to the Siege of Constantinople. The period of migrations lasted for about four hundred years.

The First Phase 300 - 500 A.D.
The first phase, occurring between 300 and 500 A.D., is partly documented by Greek and Latin historians but difficult to verify in archaeology. It puts Germanic peoples in control of most areas of the then Western Roman Empire.

The Visigoths entered Roman territory, after a clash with the Huns, in 376. Their subsequent deditio was probably not acceptable. During a dramatic incident the following year in Marcianopolis, the escort to Fritigern, their leader, was killed while meeting with Lupicinus. The Visigoths rebelled, eventually invading Italy and sacking Rome itself in 410, before settling in Iberia and founding a kingdom there that endured for 200 years. They had been followed into Roman territory by the Ostrogoths led by Theodoric the Great, who settled in Italy itself.

In Gaul, the Franks, a fusion of western Germanic tribes whose leaders had been strongly aligned with Rome since the 3rd century, subsequently entered Roman lands more gradually and peacefully during the 5th century, and were generally endured as rulers by the Roman-Gaulish population. Fending off challenges from the Allemanni, Burgundians and Visigoths, the Frankish kingdom became the nucleus of the future states of France and Germany.

The initial Anglo-Saxon settlement of Britain took place in the 5th century, when for all intents and purposes Roman Britain no longer existed.


The Second Phase 500 - 700 A.D.
The second phase took place between 500 and 700, saw Slavic tribes settling in Central and Eastern Europe, particularly in eastern Magna Germania, and gradually making it predominantly Slavic. In 567, the Avars -alongside the Lombards - destroyed much of the Gepid Kingdom. The Lombards, a Germanic people, settled in northern Italy in the region now known as Lombardy. The Bulgars, people of either Turkic or Iranic origin who had been present in far Eastern Europe since the 2nd century, conquered the eastern Balkan territory of the Byzantine Empire in the 7th century.

During the early Byzantine–Arab Wars, the Arab armies attempted to invade Southeastern Europe via Asia Minor in the second half of the 7th century and the early 8th century, but were eventually defeated at the siege of Constantinople by the joint forces of Byzantium and the Bulgars in 717–718. During the Khazar–Arab Wars, the Khazars stopped the Arab expansion into Eastern Europe across the Caucasus.

At the same time, the Moors (consisting of Arabs and Berbers) invaded Europe via Gibraltar, conquering Hispania (the Iberian Peninsula) from the Visigothic Kingdom in 711, before being halted by the Franks at the Battle of Tours in 732. These battles largely fixed the frontier between Christendom and Islam for the next millenium. The following centuries saw the Muslims successful in conquering Sicily and parts of southern Italy from the Christians, although never consolidating it.
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