Most of the pizza available in the USA is only distantly related to honest, authentic Italian pizza (and yes, I've had pizza in Italy, also at an Italian restaurant in southern Switzerland).
Also, "American" pizza covers a wide range of styles (one of which is fairly close to the Italian style, but it's not a common style). So yes, I'd say the pizza that is commonly served in the USA is an American dish. Note that this is not uncommon - much of the ethnic food available in the USA is only distantly related to the original - it's been adapted to be more acceptable to the typical American tastes. Further, this doesn't just apply to the USA. I lived in Indonesia for a while and I know Indonesian food. Several years ago I had a business trip to Amsterdam - there was an Indonesian restaurant next door to our hotel. What we were served was Indonesian in name only
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BTW, I love pizza - but the idea of MRE pizza sounds repulsive...