You two are overreacting. It is not truth to say that America owes its independence to France or any of those other countries, you are right there (though I'm not sure The Americans would have won without their help). But don't blow up at a random comment containing a personal opinion. It is a very legitimate opinion, and though it could have been said in a more tactful way, he did nothing to break any rules. Take care you do not do so either.
All the same, be sure nobody is posting potentially antagonizing things; I don't want to see any stupid arguments.