What are the main changes in civilization in the 4th century?

We are talking about the period from 300 to 400, the changes were mainly in Europe and the Roman Empire:

Civil war in the Roman Empire and the adoption of Christianity by Emperor Constantine in the year 324 (allowed from 313), and even earlier – in 301 AD. Christianity was adopted by Armenia. In 325, the Council of Nicaea took place, the transfer of the capital to Constantinople.
The division of the Roman Empire into two parts and the first campaign is ready for Rome.

In Asia, there were such changes:

Around 320, the Gupta Empire and the Pallava state appeared on the Indian subcontinent.
The emergence of the Yamato state in Japan.
The movement of the Hun tribes to the west, the beginning of the great migration of peoples.