What it says on the tin - what has to happen for this to be possible (i.e. a major world alliance consisting of at least 75% of the countries in the Americas, with the US foreign policy aimed at that instead of partners in Europe)? I would imagine the POD has to be before the 1930s, perhaps this belongs in before 1900, but I'm looking forward to seeing what everybody has.
Does this improve the station of several countries in the new world? I figure if things shake up differently you'd essentially have an alliance where America is the clear top power followed by Brazil and Argentina in terms of prosperity and influence, but that might be different here.