definition of national origin of a film?

[Gbpxl]

Probably a dumb question but what makes an American movie an American movie? If it were shot entirely in Ireland by a Mexican director and financed by a Portuegese studio and starring all Japanese actors who are all speaking Chinese and the film was only released in Brazil, would you say "oh thats a Portugese movie." or "thats a Brazilian movie."

In many listings in Leonard Maltin's movie guide, there are movies listed as U.S.-British, for example. Or French-Canadian. etc