Suppose the United States has a comparative advantage over Mexico in producing pork. The principle of comparative advantage asserts that

This principle states that a country has a comparative advantage in producing a commodity if the opportunity cost of producing that commodity is lower than the other country in terms of other commodity.

There are two countries: United states and Mexico and United states has a comparative advantage in producing pork because the opportunity cost of producing pork in United states in terms of other goods is less than the Mexico.