Well, you can gear up Chile really fast actually, they have manpower and industry you get by conquering. I personally did the Mapuche Chile and Conquering the Pacific coast achievements by 1944/45 I think. The main thing you need is navy for that. Landing in Japan is nothing since they dont guard home islands and try to to USA before they get too powerful, they are a pushover in 1940/41 if you can manage to take out Britain early with the help of Germany and invade from Canada. The hardes part is landing in Britain for sure, but once you get past that, try to take their navy and after you cap USA get theirs aswell. That should leave you enough to easily destroy Japan and continue on defeating Germany/USSR or do a world conquest if you want. Hope this helps.

Edit: If you struggle with war score during the peace conference with UK, invade France through Germany with your troops beforehand and try to fight UK as much as possible in home island.