What do anthropologists call a story that is told about the founding and history of a particular group to reinforce a common sense of identity?

Origin myth

Explanation:

An origin myth is a story that people of the same culture share that provides an explanation of how and why they came to be. All the traditions and customs that the culture has is the result of the origin myth. This unites the people by claiming that they have a common origin

The explanation provides comfort in the situation society is in.

Hence, the question here is referring to Origin myth.

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