At a length of 5,522 miles (8,891 kilometers), Canada and the United States share the longest non-militarized border in the world. Today we think of the two nations as the friendliest of neighbors, but at one time both nations had somewhat detailed plans for attacking one another... just in case.Damn Interesting: America's Secret Plan to Invade Canada
The U.S. plan was titled 'Joint Army and Navy Basic War Plan -- Red,' and it included plans for the invasion of Canada by the United States as part of a larger worldwide military action. War Plan Red was actually designed for a war against England and its Commonwealth. The scenario imagined a conflict between England (code name Red) and the United States (Blue) fighting over vital international trade and commercial interests.
Hat tip: Larry Bernard.