I checked the stats for the Fortress America Players Association (
fapagroup : Fortress America Players Association) and its 43.7% USA to 56.3% Invader victories.
What we've generally seen is that the USA is a bit harder to learn to play, because most strategy games reward agression, but the USA player must perform a slow tactical withdrawl with precision counter attacks, and maximized felexibility in unit positioning to be available to multiple fronts.
I can't imagine the Invaders winning against a good USA player with the southern Invaders heading for florida (of course, I haven't seen it, so I could be wrong). A good USA player won't let you past D.C. and Atlanta in the East, and will basically allow the west to advance 1 territory at a time by denying the helo special move with a row of defensive positions 1 space beyond the adavnce. It usually comes down to whether Blue & Yellow can capture & hold Memphis, St. Louis, and Kansas City, while red hols Florida, Atlanta, and DC.
Come test any theories about an unbeatable invader against some of our veteran players. BTW: Not all matches have to be ladder matches. Many new members of the group will play a few "friendly" games before challenging someone to a ladder match.