I played United States with New World Order Mod, and it started the game with no army at all and only about 90 manpower. In constrast, without the mod U.S. starts with about 35,000 manpower and about 20 land divisions. I built ships of various sizes but I could not deploy any of them. The production screen said I did not have enough manpower to deploy one destoryer. If I remember, the U.S. had the 17th largest army in 1936. Still, the mod seems to make the U.S. unrealistically helpless militarily.
However, when using the mod the U.S. is vastly more politically active. Without no mod, the U.S. earns 0 politcal points per day. With the mod, the U.S. gets .6 political points per day. Even though U.S. was isolationist, it would seem U.S. would have some political influence so the mod makes thing more historically realistic in terms of politics.