I agree that the Vietnamese, or at least a civilization from Indochina should be included, as that region is usually included today in the list of Cradles of Civilization. Besides, the Ankor Wat is included, but no civ goes with it.
Maybe give them Philosophical and Industrious.
I do also miss the Iroquios, because, well, if you're going to include the United States, you might include the Iroquios Confederation, from whom much of our system of government comes from - Franklin was no dummy, he knew a good thing when he saw it. Say .... Organized and Spiritual.
The Irish are about as mishmashed as the English when it comes to who they are (Angles, Saxons, Jutes, Norse, Normans, etc.) , but what precisely is American? We may dislike immigrants in this country - from the Know Nothing party of the 1800's to the current bigoted laws about ESL in public schools - but damn near all of us in this country had ancestors who came over on 'the boat', and not everyone came over from Europe.
Still, I think a better civ would be the Celts - which includes the Irish, as well as the Scots, and precursor civs like the Iberians and the Gauls. Gotta be Agressive and Exansive, maybe Agressive and Spiritual.
The Zulu should be included - a two move spearman with an automatic strenght bonus (lets face it, the Zulu would be Agressive) would be a very good special unit.
The Minoans might also be an excellent addition - start them with .... the tech that makes stonehendge, and fishing, and make their special a slightly stronger galley, say str 3 - since the Egyptians where always getting attacked by "the Sea People". They'd be Philosophical and Financial.