Why do Americans not learn about other countries in school? OK Maybe I need to back up, because many Americans do not even realize that other countries have their own histories, nor do they understand what American history has to do with the histories of other countries, such as Canada for example.
Now this is going to seem a bit rambling, because I want to discuss why some maps should show neighbouring countries or states and some do not, and really don't need to. Then I will get back to why it is often necessary to study some of the history of neighbouring countries to understand your own history.
I am often amazed looking at US TV station weather maps, where the weather is shown on a map of the USA, but on the other side of the US borders, no weather is shown. Remember the stations we get here are from Detroit, Erie and Buffalo, all places either on the border or across the water from Canada. You would think they should be concerned about what the weather is only 40 km away. In my opinion, weather maps should not stop at any borders.
Road maps are the opposite, but for a good reason. If you are producing a road map of one state, you do not need to put all the roads in neighbouring states. This makes sense, because you are expected to buy the road map of any state you are travelling to, if you want to see all the roads up-to-date. Another situation I remember, I was in Mexico talking to some travelling motorcyclists from Texas about the best way to get into California from Ensenada, Mexico. I suggested Tecate as a border crossing that was easier than Tijuana, especially since they were heading home to Texas from there. They looked at their Mexican road map and said Tecate was no good because there were no roads leading from the border checkpoint into the USA. I told them that yes indeedy there were roads in California, and if they wanted to see the roads on the California side they should get a California road map. It is quite normal for any country or state to produce road maps that cover their own roads, but not all the roads in bordering states. When travelling in Ontario, for example, the 401 says "Windsor 250 km". It does not say "Detroit 252 km". That does not mean Detroit does not exist, nor does it mean Windsor is more important a city than Detroit. You are just expected to know that Windsor is the border city near Detroit and get a Michigan map to continue your journey. They do the opposite with road signs on the US side of the border.
Now back to history. What could Americans possibly learn about their own history by learning about the history of Canada? First they would learn that Canada has repelled several US invasions, especially if you count some of the fighting that went on before the USA got its independence from Britain. The second thing that you could learn is that many English speaking Canadians are descendants of refugees from the US war of Independence. At one time, just after the war of independence, the number of American refugees in Canada was so great that they became a majority of English speaking Canadians.
Here is the next question. Why do Americans not want to know about this part of Canadian history, which actually seems to be an integral part of their own history? Well, apparently some Americans did want to teach this part of American history. The part where Americans who were loyal to the British were forced out of the country after Independence. But other Americans decided that this part of their history should be buried, covered up, for the sake of national pride.
After WW1. Charles Grant Miller, a writer for Hearst Newspapers, (forerunner of Fox News), started a campaign to rid America of unpatriotic history books. In particular a book called "An American History" by David Saville Muzzey. The Muzzey book had its flaws, for example a quote from it about native Americans reads "a stolid stupidity that no white man could match". But that's not what caused the hoopla. It was the part of the book that suggested some Americans, before the war of independence, considered themselves as Englishmen, and supported the King's government. That was the part that was treasonous to America.
(Ref "History on Trial", Nash Crabtree and Dunn, p. 25-28.)
Further reference online
But once you remove the reference to loyal English-Americans from US history, how do you explain Canadian history? And how can you explain the American defeat in the war of 1812, in the attempted conquest of Canada? You can't, so you just better ignore that invasion altogether. And how do you explain that Canada started fighting Germany before the USA did? You can't, so you ignore the war before 1941. How do you ignore the part played by France in the US War of Independence? You can't so you just belittle the French generally to make yourself feel strong and brave. That's why teaching "patriotic" history requires large doses of ignorance.