Why would nomads raising cattle on dry grasslands want to migrate into South Asia

Explanation :phuntsok Dorje makes a living raising yaks and other livestock on the vast alpine grasslands that ... says Tibet's climate is the most sensitive in Asia and influences the globe. ... but residents say their economy has dried up along with the nearby wetlands.

a social contract.

"a social contract is an agreement between citizens and their leader where the citizens give up certain freedoms in exchange for protection. the constitution of the united states is an example of a social contract."