Why did the nomads stop at the Indus Valley and decide to stay there?

Many scholars believe that the collapse of the Indus Valley Civilization was caused by climate change. ... By 1800 BCE, the Indus Valley climate grew cooler and drier, and a tectonic event may have diverted or disrupted river systems, which were the lifelines of the Indus Valley Civilization.

answer; the best answer is (demand);

for many centuries there were important factors which the economies of the muslim empires developed increasingly. they applied economic procedures in production, investment, finance, taxation and property. they used to tax certain goods (for example: harvest), they charged interest on money lent, they signed contracts with merchants; they relied on a common currency, and they used checks as well as promissory notes. with the money collected by means of taxation, the government provided the needy with an income. in addition, trading networks covered huge distances, so far regions started to have contact and exchange goods. this trade network covered areas of asia, africa and europe.