That applies when your model of a country is on the scale of something like Switzerland or Ireland, which is to say something on the scale of Pennsylvania or Colorado.

The US is more on the scale of a continent than a country.

Economics isn't science, and while Ricardo has some brilliant insights, it isn't a science; he barely models anything. It isn't even a hypothesis since you can never really test it. The core of his idea is this:

the rate of profits can never be increased but by a fall in wages [...] If, therefore, by the extension of foreign trade, or by improvements in machinery, the food and necessaries of the labourer can be brought to market at a reduced price, profits will rise.

I.e., use trade to get to lower wages