Theordore (he detested the vulgar nickname, "Teddy") Roosevelt also hoped to conquer Canada to obtain room for all those gazillion Americans he hoped to add.
But since America hasn't acquired lebensraum in Canada and appears unlikely to do so in the future, we have no more room for any more people unless you like being forced to share and forced to take turns by more government and more laws regimenting your existence.
I would rather be free.