1. first priests 2. second peasants 3. third warriors 4. fourth secretaries.

Priests are #1
Warriors are #2
Secretaries are #3
Peasants are #4

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Priests.Warrior.Secretaries.Peasants.

Explanation:

Priests: were very important people in ancient times they also know as the messenger of God on the earth, besides serving to the god priest did many other jobs such as spiritual teaching and conducting ritual ceremonies.Warrior: were very important for the protection of the empire, warrior shows great courage, vigor, sacrifice, and aggressiveness against an opponent to achieve victory.Secretaries: were other important people of any kingdom or empire they help the king or ruler in maintaining various ministries in the empire.Peasants: comes at the lowest level in society, lord or ruler offer protection to peasants in return peasants get living and work on lord's land.

The answer is ethnic groups.