Why is any periodization of human development conditional?

Because it is divided into certain periods and there are no clear terms for the transition to a new one. The very periodization of the development of mankind can be divided into such time intervals:

1) Primitiveness – occupied the period from 3 million to 3 thousand years BC;

2) The Ancient World – covers the period from 3500 BC to 400 AD;

3) The Middle Ages – the time period from the 5th to the 15th century;

4) Modern times – the period from the 16th to the 19th century;

5) Modern times – the period from the 19th to the 20th century;

6) Modernity – the period from the 20th century to our time.