In the past when men's needs were few, it was not necessary to get things from distant lands. But today, the people of one country depend on the people of another country for a variety of things. As a result, world trade has developed. Without world trade, it would be difficult for the people of any country to get many things which are now considered necessaries. Some countries are not rich in mineral resources. They have no iron or coal mines, while others have too many of them. Again, some countries are not suitable for agriculture while others have several fertile plains to grow crops. Further, even if a country is rich in natural resources, it may not have enough skilled men to exploit them. So, people around the world learn thatthey cannot produce profitably and to sell things for which they have a special ability to produce.