In the 3rd century CE, The Roman Empire started to face its downfall. With increasing pressure from the Germanic tribes and internal disputes, their constantly changing generals as emperors were quickly deposed by rivals. This continued till 285 when Diocletian rose to power.
He along with Constantine organised the Roman Empire. They brought in Christianity and it soon became the Roma state religion. This was under Theodosius who ruled between 379 and 395.
During this time, the Germanic tribes kept attacking and tried to invade the Roman Empire. These occurrences took place in the battles with Sassanids as well as the Gothic invasions which were spurred by the Huns. Due to these attacks, there was an increase in migration into the heart of the Roman empire.
After the death of Theodosius, the Easten Empire started to evolove. It became Hellenised Byzantium in the seventh century. The Roman Empire also underwent food shortages multiple number of times, deposed its emperor and sacked Latin Rome.
There were attempts to take back the Roman Empire by the Eastern Emperor Justinian. He also tried to conquer North Africa and Gaul. However, this effort was in vain because of tax burden and the Lombard invasions Italy. The Byzantium consisted of a part of North Africa, Nilotic Egypt, the Mediterranean Islands, South Balkans, Thrace, Anatolia and Levant by 600CE.
The Franks occupied Germany and France while the Visigoths had their control over Spain. The Angles and Saxons had Southern Denmark and western Britain under their control.
On the political front, Byzantium had to confront the problem of the Avars. The Sassanid Persian attacks cut off Byzantium from Eastern Anatolia and Levant which was the birthplace of Christianity. Heraclius who ruled from 610 to 641 defeated the Sassanids. However, the empire’s military was over worked and exhausted trying to establish control over the East.
Due to this, the Muslim invaders arrived from the Middle East and got rid of the Byzantines. Their mission was to eject the Byzantines all over the Middle East including Anatolia. After their success, Stuck between the Avars who were ruling the Balkans and Adriatic regions and the Arabs in the Roman lands, the Byzantiums began to propagate an orthodox form of Christianity as a retaliation to Islam which was a growing concern in the West.
During this time, the Lombards in the West, along with other tribes had an alliance over the control of Italy. France was spilt three-ways between the Burgundians, Visigoths and the Franks. France was given to the Franks and the Merovingian dynasty of Clovis was established from 482 to 560s.