International trade has been a thing as long as there have been multiple nations aware of one another. International trade occurs because resources are not evenly distributed amongst nations. Different nations have different amounts of natural resources that make producing different types of products easier or harder depending on the area of the world.
Even within different countries this can be seen as different regions have different environments that allow for the production of different things. A large amount of the fuel used in the United States is imported from Middle Eastern countries, for instance, because those countries produce a lot of oil.