It's interesting to think what the transition point was when people just made do with whatever plants and animals were available nearby, and that was "food," to when things became "<country/culture/region/etc> food." If tortilla wraps, beans, etc. were imported to Japan 300 years ago, that would just be Japanese food, but now if a Japanese restaurant started mixing those in, it would never escape the label "Japanese/Mexican fusion" or a variation on that.