Not only Mexico but several other Latin American former colonies also started independence movements back then, by the way...
But well, perhaps going back to 1810 may indeed be too much to ask, granted that Napoleon is still running around and whatnot, but 1816 or 1820 seem like good dates to give the player at least some possible (even if realistically fragile) chance at, say, preventing / reversing the revolts in Spanish America, while not going too overboard....