It's great if you want to be self-sufficient pending a great war. The way things are going, it may be the only thing to justify such blatant self-sabotage, and hence necessary to start one.
If you think a war is coming, why would you antagonize your closest allies?
Building up strategic industries is another reason.
Or, in America's case, arresting their decline.
It can be a self-fulfilling prophecy : “We have to go to war with them because they retaliated with tariffs!”
Trump has literally said that if Canada doesn’t like the tariffs, they should just let the US annex them!
Well if you do all you can to stirr some 'great war', you will eventually get it. Its only US saying there will be one though, rest of the world is in WTF mode. China doesn't care about anything global but Taiwan and its own security. They are probably more capitalist than US at this point and prefer having stable trade cash flows rather than expanding.
So, if thats the real underlying reason for all these steps then US is the warmonger here attacking literally everybody preemptively. 5D chess at least.
If you make everyone rely on each other, war hurts everyone more and is more likely to be avoided. If going to war doesn't cost you a supplier, war is more palatable.
Global trade reduces war