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In this timeline I'm working on right now (with a PoD of 1847), the USA allies with Germany and declares war on the Entente during WWI (the Entente consisting of Japan, the Ottomans, Britain and France). Now, when the US declares war, the Brits would declare war back. When that happens, all of Britain's overseas realms (like Canada and Australia) would probably follow suit, yes?

So, if I'm right, the US is now at war with Canada.

How would that go? Where would the US attack or invade? Or would Canada be doing the attacking? Also, what would Mexico be doing?
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