Why do historians believe that the peoples of Ancient Indus and Ancient Mesopotamia engaged in business trade with each other?

When people first settled down into larger towns in Mesopotamia and Egypt, self-sufficiency – the idea that you had to produce absolutely everything that you wanted or needed – started to fade. A farmer could now trade grain for meat, or milk for a pot, at the local market, which was seldom too far away. Cities started to work the same way, realizing that they could acquire goods they didn't have at hand from other cities far away, where the climate and natural resources produced different things. This longer-distance trade was slow and often dangerous, but was lucrative for the middlemen willing to make the journey.

Explanation:

The first long-distance trade occurred between Mesopotamia and the Indus Valley in Pakistan around 3000 BC, historians believe. Long-distance trade in these early times was limited almost exclusively to luxury goods like spices, textiles and precious metals. Cities that were rich in these commodities became financially rich, too, satiating the appetites of other surrounding regions for jewelry, fancy robes and imported delicacies.

first of all, it's important to say that the book we shall not be moved, written by joan dash, is about the first strike of women in the united states in the year 1909. the best historical detail to clarify the reader's undertanding is the phrase "general strike". this strike involved women working at a garment factory who decided to protest   long working hours, low wages and brutal conditions. this strike became known as "the new york shirtwaist strike" or "the uprising of the 20,000". the strike mostly involved jewish women who did not speak english or who had a basic knowledge of the english language. finally, the strike went on from november 1909 until february 1910.