Everything is a composite. I think the only meal I've ever had with no outside influence was a roasted sheep and fermented mares' milk in Mongolia. Everything else has influences from somewhere else--some going back to 3,000 b.c., some not much further back. I got into a discussion once with someone who insisted that she only like authentic Mexican, such as tacos al pastor, but I pointed out that al pastor is essentially shawarma and was introduced into Mexico by Lebanese immigrants in the beginning of the 20th century.
That said, since bacon was invented in about 1,000 b.c., by the Celts, I think one could make a case for carbonara predating WWII (and I've heard at least one lecture that takes it back across the centuries.
But yes -- everything is a mixture. Poland got pierogi from invading Mongols. The word haricot in France's haricots verts is a corruption of a Nahuatl/Aztec word, because that's were the beans came from. The tandoor oven was introduced into India from Central Asia. And the sunflower, which is so vital to Eastern Europe as to have been made the national flower of Ukraine, is from Kansas.
So there are very few pure, untouched cuisines on the planet--but trading and trying new stuff is very authentic.
Plus it's worth remembering that even Italy, as an actual country, didn't exist until 1861--it was a cluster of independent city states.