A half-baked thoery that the USA could do as the fuck it liked. In practise, it got land and the begginings of an empire by paying for it before it started a revolution against the European powers that owned it. When the USA did try and annex Canada, a small number of the British army and a few thousand Canadians beat off the
United States, leaving ti with the option of the treaty of Ghent, which didn't give them any land concessions (as opposed to the British-Canadian forces, which never intended to make any, so handed back all taken land without grudge) nor did it make either side any richer. As a courtesy, the Royal navy ended impressing.
When the
united states wanted to start an empire, it went after a weakened spanish empire, which was
on the brink of freeing itself. When the USA again attempted imperialism in south america, it was having a little trouble with fallen power Spain, so decided to pay $20,000,000 to buy a few POS nations that would have revolted in a few years anyway. Wow, isn't that clever?
Obviously, these places have since gained independance. Quite possibly the worst empire ever...