What if the Roman Empire had survived the barbarian invasions after 4th century? What if the Eastern and Western Roman empire had been reunified? What if this empire would have developed into a strong industrious country?
In this alternate history experiment this process will be described in more detail.
The 5th century
With the death of Emperor Theodosius 395 AD, the Roman Empire was divided into the Eastern one, ruled by Arcadius, and the Western one, ruled by Honorius. The official religion is Christianity. The Eastern Empire is more populated and has a more powerful economy. It survives the barbarian attacks by paying tributes to Attila and other leaders. Meanwhile, the Eastern half of the Empire is invaded by the Germanic tribes and soon loses all its territories in Britain, Gaul, Hispania, Africa, and almost all Italy. In 410 AD the Visigoths reach the capital of the Western Empire, Rome. The eastern regent Anthemius had anticipated this and had sent an army of 10,000 soldiers in 409 AD to protect this very important city. Although the Visigoths have a greater army of over 40,000 men, and the Romans only about 30,000, the invaders are defeated by the more professional army of the empires. This way the Western Empire can reconquer some territories in the Italian Peninsula with the help of the Eastern Empire until 450 AD. Also Emperor Leo I (457 - 474) contributes sending an army of over 15,000 soldiers. The two empires fight together in the battle of Mediolanum in 483 AD and reconquer the territories around the Po. With this campaign Dalmatia also fall to the Eastern Empire.
The Emperor Justinian I, who ruled over the Eastern Roman Empire from 527 to 565, changed many Roman laws and tried to expand Latin in the eastern regions, which were dominated by Greek. He improved the communication between Rome and Constantinople, building effective horse stations where messengers could change their horses and so be more faster. He built several academies in the Balkan territories and in Italy, with the goal of improving the economy end education there.