The map does not break by accident. It breaks because one republic prepares better, marches harder, and learns how to turn invasion into administration before British North America can catch its breath. Roads, rivers, garrisons, proclamations, supply wagons, and tidy military logic do what bluster alone could never do.
Volume I opens the fracture at the point where conquest stops being a raid and starts becoming government. The question is no longer whether Canada can be taken. The question is what taking Canada does to the United States, the British Empire, Indigenous nations, local families, future rebels, and a continent that thinks it can absorb a broken border without paying interest.