The BGG description says that there are 4 factions. The blurb isn't exactly clear but it sounds like:
1) Americans (regulars and militia)
3) British regulars and Loyalist militias
The map shown tells a different story. There are 5 different color units shown, which would mean 5 factions. Based on the locations of the different factions, I'd guess:
1) American regulars
2) American militia
3) British Regulars
4) Loyalist militia
If that's the case I'd see French and Hessians simply being reinforcements for the American Regular and British Regular factions respectively. Of course all that's just speculation on my part.
So what is the story? How many factions are there in the game and what are they?
If I recall correctly, the Hessians and French are not any of the factions and only come into play after the approprate card has been used. The Indians on the board are neutral until a faction moves into their region and takes control.
The four factions are, American Regulars, American Militia, British Regulars, and the Loyalists.
P.S. I played the prototype with Uwe at Gencon, I hope my memory is not faulty.