In the 1930s, the United States Army War College developed hypothetical war plans for a possible war with Canada; they featured an invasion in War Plan Red; it was merely an academic exercise. Similarly, Canada developed Defence Scheme No. 1 to counteract an American invasion.
- from Wikipedia
If he was being honest with himself, Alfred could admit that he didn't really think Matthew would attack him. They'd kind of sort of had a taste of that in 1812, and it wasn't like it had been fun. Or productive. Or really anything other than horrifying and full of smoke and ash and, in its own warped way, just as bad as fighting Arthur. Maybe even worse, because he'd expected Arthur to be tough. But Matty was kind of a doormat. He didn't really… intimidate people or anything.
It was just that, well, Canada was part of the commonwealth, and right smack dab up there. It was him and then Mexico down south, and he already had a contingency plan for Mexico. Not that he was really so worried about that, either, but he was the country bordered by the both of them, now wasn't he? He was in the middle of the sandwich if they snapped and decided to try and conquer him. A hero was always well-prepared.
Fortunately, even though his military had their own plans for what to do in such an event, Alfred knew one fool-proof way to really stop his brother if he ever got any funny ideas. So he fetched himself a big wooden board, and some black and white paint, and went to work. When he was finished his hands and sleeves were covered in paint splotches, but he just nodded in approval and then dragged his prize up along the road, and kept going until he was within spitting distance of the border. Then he got out a hammer, and a post, and some nails.
A few minutes later, he stood back and put his hands on his hips. There. No way was a Canadian army getting past that.
The plank of wood – painted white – read in big, block letters:
PLEASE DO NOT INVADE.
Later, they would say that it didn't happen because there wasn't any reason for it to happen, and that World War II had strengthened the ties between nations, and all of that.
But Alfred liked to think that the sign had really sealed the deal.