It was hardly a trade war. It was one MP that thought that maybe this would be a good idea and the US going "er, maybe". The UK is such a non-market as far as the United States is concerned, especially once you calculate in all of the costs of shipping, that it was never really going to happen.

The only real reason that it got brought up so much was that it was a good demonstration of the utterly delusional attitude of brexitiers. That somehow we'd be better off with lower food quality standards and that should be something we would celebrate. I do not think it got much further than the vague idea stage because it really wasn't viable for the United States so they never agreed to it. No matter what some nutcase MP may have thought.