that's how it's supposed to work. You're right that US is not a signed member of the ICC.
Also i hope america is not so far corrupt that they would consider their politic advisaries as enemies. Either way it would be an international court that would convict or acquit a person of a war crime. If your political adversary is not guilty of anything then the case won't even be brought i hope
As I said, the ICC is a political tool, it's wielded as a cudgel against political enemies. It's not the USA that is so corrupt(at least in this case), it's Europe.
As i already wrote, they are beginning to.
Hypothetically sure if a country and it's citizens are completely fine being shunned from the world i guess that could work. No country on earth does it better alone though.
Depends what you mean with collapse but technically yes! Not immediately ofc, the economy would collapse first and prices would run rampant. You know that US is the largest importer of goods in the world right? They don't do that just for the hell of it, it's because it benefits them otherwise wouldn't be a point in the trade to begin with.
All America has to do to ensure the collapse of Europe is to withdraw from NATO and recall all military assets in Europe. This would be bad for America, but the entire European continent would set itself on fire and fan the flames for another thousand years. They're totally incapable of defending themselves. They couldn't do anything about it either, so crippled by the sudden need for military spending that any thoughts of retaliation through sanctions would be throwing gasoline in their own wounds and lighting it. Lol maybe America stops ensuring safe passage for your merchant vessels also, and piracy runs rampant. Now not trading with America has forced you to stop trading with most of the rest of the world.
America profits immensely from relations with the entire world, but everyone else profits much more. War in Europe didn't end suddenly after thousands of years because they all suddenly became peaceful, it ended because America made it impossible to wage war in Europe.
For America to destroy Europe not a single shot needs to be fired, nor any aggressive action taken. It's fkin astounding how Europeans feel so confident on their high horses throwing rocks from their glass houses