Trade is necessary to promote survival of a region and its people. Those involved in trade send goods that they have an abundance of to other regions in exchange for money or other goods that they do not have enough of.
Trade agreements between regions can promote a better economy for both parties involved. Trade is responsible for thriving regions because it provides them with the money and goods that they require for the people of the region to survive. For example, a region with a lot of rice can trade with another region that has a lot of fruit so that both regions have enough rice and fruit for all citizens.