Free trade works within a nation. We demonstrated that with our history (citizens of the United States trading with citizens of the United States). We created the largest free trade area of the world. And the world was dying to get in and be a part of it.
However, to gain access to our markets and protect our own industries, they had to pay a cover charge, or tariff.
There were exessive tariffs to be sure but the best ones just evened the playing field to compensate for wage differences, cost of transport etc.
Things started to go to pot when when started bringing our tariff rates to zero as Britain, etc. did before us.
Free trade itself is not akin to marxism. The way we practiced it in the beginning of our Republic is based on Adam Smith and Liberty.
Absolute free trade, however, is first cousin to marxism because it treats everybody and every nation the same ("from each according to his ability" etc.) and does not take into account such variable as governments and their regulations, wage differences between nations, travel costs, etc.
Don't mistake Free Trade with Free Markets, they are not the same thing. We have free markets in America. China, with whom we have Free Trade (really we have free trade and China practices merchantalism defending its markets) has a lot of monopolies dominated by government figures so not trully free markets.