Everything looks pretty solid, but I think your South American alliances are off. Unless Argentina went through a very different development cycle, they're still going to be a primarily agricultural exporter, with someone in Europe as the primary market (the US produces plenty of beef and grain on its own). Unless they're mostly exporting to Germany (which would likely require some serious butterflies as well) their primary market is going to be the UK (as well as their primary source of capital). In that sort of situation, aligning with the US against the UK would be nothing short of suicidal folly. If you want the war to expand to South America, you really need an American aligned Brazil.
Also what's the world wide economic / trade situation like? Has British capital been cut out of the US? Has the US stopped it's massive trade with the UK? What about immigration to the US in general, has that gone as OTL?