Why nations are involve in trade? Discuss in brief

The fundamental reason is that the nations cannot produce equally well or cheap products all that they need. This is because of the unequal distribution of natural resources among them or differences in their productivity levels. Due to this, one nation who is better or efficient in production and have surplus products can distribute its goods to other nations. As a result, each nation finds it advantageous to produce some commodities and procure other products from other nations.