Comment by jjk166

> Given your earlier claim, surely you must believe that if they defied your wisdom and chose this course of action, they wouldn't be able to do this because they would have to devote a substantial fraction of their military capacity to domestic counterinsurgency efforts, leaving far more limited combat power to actually execute the invasion?

That does not follow. First, my scenario for how an invasion of canada would go down fundamentally assumes that the conditions preventing an invasion of canada from happening don't exist. The world where Canada must defend itself from a US invasion is a magical, fictional world where the US has managed to launch an invasion.

Further, successfully invading Canada would not require the full force of the US military, and it is not established that the resources needed for the invasion of Canada would even be the same as those required for fighting domestically, nonetheless that the resources would be required concurrently. The men and materiel necessary for disabling the Canadian armed forces and seizing key territory would in general be useless in a domestic counter-insurgency scenario, and vice versa.

The problem with civil war is not its drain on your military resources, it's that the campaign to regain control over the rebelling regions requires you to inflict destruction on your own people. A victory is inherently pyrrhic, and if you aren't careful you may breed sympathy for the rebellion in even more regions. The US should avoid civil war because it's catastrophically bad, not because it would interfere with the canadian invasion effort.