Your statement is false. Postwar Japan and Germany are but two examples that disprove your statement. Certainly Japan, which had no concept of democracy in its entire history has proved to be an excellent example of that fact that imposing democracy can work. In addition, I would submit that Japan's democracy is indeed evolving given its recent amendment to its constitution allowing posting of Japanese troops to other countries.
With regard to Germany, while the concept of voting was not foreign, the release of the German people from the grip of a totalitarian regime so that they could re-establish a participatory democracy was striking - to say the least.
While it may seem trite to say something like "America is a democracy builder", the fact is that we have been such for a number of countries. As with all things humans do the outcomes have not all been perfect. However, to impugn that we as a nation are hegemonic simply because we have not been totally successful in all our endeavors is patently absurd.
Japan had a thriving Western democracy before the rule of generals and before they had a full democracy their leaders prepared and accepted that democracy was the way to go and began a generations long drive to educate and remove class distinctions from their country.
Your statement was a waste of time.