A war would be disastrous for both countries. Especially the US.

As President Donald Trump relentlessly threatens to annex Canada, some Canadians are worried that an American invasion could one day become a reality.

How would that scenario play out? Looking at the sheer size of the American military, many people might believe that Trump would enjoy an easy victory.

That analysis is wrong. If Trump ever decides to use military force to annex Canada, the result would not be determined by a conventional military confrontation between the Canadian and American armies. Rather, a military invasion of Canada would trigger a decades-long violent resistance, which would ultimately destroy the United States.

But in this nightmare scenario, could Canadians successfully resist an American invasion? Absolutely. I know this because I have studied insurgencies around the world for more than two decades, and I have spent time with ordinary people who have fought against powerful invading armies.