Words on a page don't put boots on the ground. The treaty would be invoked, US would be expelled (and sanctioned), and nobody would dare try to break the blockade.

The only meaningful resistance would come from within the US military, or maybe China would finally venture out of their sphere of influence (although it's more likely they'll use the opportunity to pursue more regional concentration of power).

The reputational damage would be hard to understate. I think anyone with a bone to pick with the States would happily and repeatedly point to us Canadians as an example of what happens when you trust Americans. And that would be enough to achieve a lot of their regional policy goals, if not much more. Mexico would probably seek other political partners to make sure they're not next.

Yes, an American invasion of Canada would immeidately set the stage for a worldwide rationale for opposing US interests.

Annexation of Canada would mean the end of the soft power for the Americans. The only way anyone would let them in would be through hard wars.

At least China and Russia only forcibly attacked independent countries that were once united with them.

Which wouldn't matter much because Canada and Europe rely on US military, equipment, and IT and the US is an ocean away.

The US imports most of its oil while exporting the oil it produces. Ooops.

The US imports pretty much everything consumers consume. Ooops

The US would have nobody to sell anything to. Ooops

The US is now in a local conflict that a very large % of citizens does not support. What happens after the next election?

These are good points, but I have to comment that all of these suggest the physical resistance to an annexation would come from domestic actors rather than international.

Let me be clear, there are 1,001 reasons why annexing Canada would be a bad idea. I'm just saying that military impossibility is not one of them.

It is a fun fictional exercise, ala Man in the Highcastle

I think it would be closer to Handmaid's Tale than Highcastle since it's a modern day than a twist WWII ending

fun and interesting either way. I hear netflix potential

Would anyone really want to oppose America though?

> expelling USA from NATO

which would suit Trump just fine. this isn't a dissuading argument to Trump, and would probably be considered as bonus to his lot.