Question

in which civilization did mahabharata happen​

Answer 1

Mahabharata never happened. It is just a holy book or "Mahakavya"

Explanation:

It is one of the two holy epics which contains philosophical and devotional materials.

It narrates the struggle between two groups of cousins in the Kurukshetra War and the fates of the Kaurava and the Pandava princes and their succession. Along with the Ramayana, it forms the Hindu Itihasa. 

Hope it helps.

Answer 2

Indus Valley civilization

Mahabharata occured during the Indus Valley civilization.

Historical references tell Mahabharata war took place around 3100 BC.