I find that late game US is a very tough nut to crack. The AI, despite being clueless about defense for just about every other country, always manages to build level 5+ naval forts on every port and garrison them with death stacks of 40 width infantry. Not to mention air superiority that is provided by multiple level 10 airfields with overlapping coverage and 10,000+ fighters... Just no fun at all. It can be overcome, but its such a painful slog that I'll quit a game rather than try to capitulate a late-game US opponent.
The best time to defeat the US is early game, when they don't have an army and their entire defense relies on naval power.
Once, as Germany, I did this method:
Immediately justify on the Netherlands. First thing; right out of the gate. Your starting army can crush them in no time. Annex the Netherlands and especially all their territory in South America. Puppet the Dutch East Indies (keep an eye on Japan... you may eventually need to dismantle the Axis and join Japan's faction to keep them from declaring on you over the East Indies). Build up former Dutch territories in SA and the Carribean with level 10 ports, and as much anti-air, radar, and airfields as you can manage. Build naval bombers and mine-laying subs, as well as some fighters to grab air superiority. CAS are nice, and keep a few factories on them, but you can switch to mass production of CAS once the US navy is sunk. Do your infrastructure and industry focuses. Grab the naval NFs too. Do not do Anschluss, but boost fascism in Austria to flip them, then ally with them. If their opinion of you hits 100 you can annex them thru a referendum which cores Austria and avoids the WT from Anschluss. One you have a robust force of subs and enough naval bombers to darken the skies, justify and declare on Cuba. The US should honor its guarantee to protect Cuba, because you are a European country. This gets the US into a war without putting WT into low orbit. Lay mines in and naval bomb the Carribbean. As long as you contest the ocean region, the US will keep sending ships to get naval bombed. Naval bombers are noticeably more effective at hitting ships than CAS. Once you have enough naval supremacy, invade Cuba. Turn Cuba into an air field with max radar and anti-air. Use it as your staging area into Florida and the Gulf States. Set up invasions targetting multiple ports in the region. Land in the ports and push to link up your beachheads. Then push forward while building up all captured ports to level 10. By this point, the US is actively and quickly building up its ground forces, but as Germany you should have several years' head start on them in that area. You should be able to push into the US pretty quickly. Every state you capture robs the US of factories, which weakens its army. The US will collapse before too long. Puppet them to avoid having to station troops there to defend against the UK/Canada when war with the Allies breaks out, and you're done!
