No offense, but this question is kinda dumb, since we can only answer of films we have seen that have been IMPORTED to the USA. We don't know about the hundreds of films France, Germany, Italy, etc. make each year that we never see. Although I would have to say the country with the most popular imports has got to be France, and they were also the most influential, from Truffaut's "Politique Du Autuers" forever changing film history.