How do historians divide the past into periods? Do they face any problems in doing so?

Historians divide the past into periods on the basis of continuity. This continuity is further based on:

1. Coins
2. Inscriptions
3. Architecture
4. Textual records

But they face difficulties in doing so as discontinuity exists.

1. Textual records increased tremendously.
2. They gradually displaced other types of available information.

Thousand years of human history (or of any country or region) witnessed a number of changes. After all, the ancient history of India is different from that of the other two periods i.e., the medieval period and modem period. Therefore describing the entire period as one historical unit is not an easy task.