As France, I invaded Mexico when given a casus belli by the event.
PhilThib mentioned in an earlier thread that once France occupies all of Mexico's city, there should be an automatic white peace, with France receiving a lot of Prestige and a puppet government.
I have occupied all of Mexico's cities for twelve turns now and nothing has happened.
I must say the rebels are quite a challenge, as is keeping your troops supplied in the arid north or the southeastern jungles. Even troops armed with superior rifles will lose if their supply and cohesion is too low. It is beginning to feel like a nineteenth century vietnam, but I still have all the cities, and the peace event should fire.