Why does modern mankind need a world economy?

Today no country can provide itself with everything it needs. Therefore, it should be a member of the global economy. In some countries, minerals are mined. Others process them. In third countries, the necessary devices and gadgets are made from the raw materials obtained. The same applies to agriculture. Some countries are famous for their wheat. While in others, coffee or tropical fruits grow in abundance. Only by cooperating, each of the modern countries can receive all the benefits of civilization.