Most of their atry should stay in cities fortified. Hence, if we don't end the turn move of the army near a city, it might be OK. Hope they don't get bombers. Hope they don't have rubber. Hope they don't have oil. Hence, we battle mostly with rifles and this can be accomplished. Once we pillage roads on Amercian continent, it would be easier. They won't have luxuries and would stop research.
American navy as well as Mongol might be powerful, so it would be nice to have lots of galleys especially veterans for cover up and regulars for transporting. Well, it looks scary indeed. Better leave them alone. May be they revolt to fascism and stop researching. Still Washington is a good candidate for 20K victory.