Turn Romania in to fascist, invade Hungary and Bulgaria ... defend against the Reds
My Game Winning Mexican Dominance Strategy:
I'd buddy up with the US and USSR while reforming my government to Communism. I'd then get support up for an invasion of Central America (Those are rightful Mexica lands and will be taken back!), after which I'd invade the Caribbean while setting up the "Sociedad de las Naciones Hispanos" a faction that I hope to include all of Latin America and Spain with. If not then the Comintern will be my faction in which case I'd try to take over Latin America before reconquista-ing the USA.