Free trade has little impact on monopolies. The biggest corporations in the US are international and the massive amount of free trade we've had from Reagan to Trump's second term has only resulted in these companies becoming even more consolidated.

What free trade enables is for monopolistic corporations to take control of foreign resources to circumvent and undermine US labor laws. They'll buy the rights to the same crops growing in Mexico or Candida for cheaper than the US to undercut US farmers. None of that changes the price they are selling goods in the US and in fact ultimately results in prices going up in both Mexico and Candida.