America had an opportunity to take all of Mexico, but declined to do so. I can't remember the years, but it was after the Civil War.
During the Revolutionary War, the Continental Congress sent a contingent to Canada precisely to ask for their support in fighting England. And if they agreed the American colonies offered to make them the 14th colony and they would be given complete freedom of religion. The Canadians thought about it and said no.
Wasn’t that during the Mexican American war in about the 1840’s?