Evolution of farming emerged independently across many clusters around the world and along the Indian Ocean rim. The evolution of Indian Ocean rim along is about the evolution of these clusters & their long distance interactions from very early stage.
Around 4500 BC, the Sahara & Arabian grasslands began to dry. Populations that were living in the encroachments began to converge along the Nile in Egypt and the Euphrates & Tigris in Mesopotamia. There were already farming communities along these rivers. North western parts of Indian subcontinent also become drier while witnessing increased activity. This increased pressure on land might have led to developments of political & cultural institutions along the river cities.