There is a strategy for attacking the US with Germany and Japan. Everything has to go right and you could probably only get away with it one time because it relies on a surprise. Once you do it, it’s something the US player will probably be watching for.
Turn 1 = Germany = Attacks Paris and Royal Navy in sea zones 109, 110 and 111. Purchase a carrier and either 1 destroyer and 1 sub OR 2 transports. Also take Yugoslavia, Bulgaria, Finland and Normandy. With the new territories, national objectives and plunder of France’s treasury, you should clear 70 IPCs to spend round 2.
Turn 1 = Japan = Build 3 transports + 1 artillery. Make attacks in China but don’t provoke Russia or the Western Allies. Gather fleet in SZ 6.
Turn 1 = Italy = Try to destroy Allied ships while trying to protect as much fleet as possible. Take Greece and if Germany doesn’t take S. France, take that too.
Turn 2 = Germany = Purchase 10 transports and move enough infantry, tanks, artillery and/or mechs to fill them to Western Germany. Any troops not earmarked for the transports should start moving to the Russian border. If any Royal Navy still exists, kill it. Use some Luftwaffe to help Italy clear Allied ships out of the Med.
Turn 2 = Japan = Buy more transports and equipment and troops to fill them. Continue attacks in China.
Turn 2 = Italy = If Med is cleared and opportunity arises, send your troops to take Egypt. Otherwise perhaps take Syria. Whatever you do with your army, end your turn with whatever warships you have left in Sea Zone 92.
Turn 3 = Germany = Purchase infantry and other units to defend Eastern front. UK should be thinking you are trying Sealion so they have probably been buying all defensive units on London. That means no Royal Navy in your way. So, you take your navy and transports and shoot down to Sea Zone 91 and take Gibraltar with that Naval Base.
Turn 3 = Japan = You could purchase more transports + units to fill them. It’s up to you. Main thing is taking your fleet and all your current transports from Sea Zone 6 to Sea Zone 1. Land a few units in Alaska and the bulk in Western Canada. If the US player put a blocker in any sea zone between Japan and Western Canada/Alaska, you will have to send your warships to kill it first and invade next round.
Turn 3 = Italy = Important thing here is any warships you managed to have in SZ 92 go out to either SZ 102 or SZ 89 to clear any US blockers.
Turn 4 = Germany = Now spring the surprise. Everything in SZ 91 goes to SZ 101 and invades the Eastern US. Even though Japan’s attack on Turn 3 put the US on a war standing, they will still only have their pre-war income to spend on defenses. You will be attacking with 11-13 transports full of land units to attack them with. That’s 22 - 26 land units! Most likely the US will not have enough to withstand your assault. Meanwhile, keep trying to pile up defense on the Russian border because Stalin will come calling.
Turn 4 = Japan = Invade Western United States from Western Canada. Also take that mighty Imperial Navy and attack whatever fleet the US managed to build and stage in SZ 10 or around Hawaii. Assuming the Germans take the US capital, this attack will give Japan a nice 10 IPC territory and eliminate the main threat to your expansionism. UK and ANZAC will have a little fun at your expense for a round or two, but once you get back into position you will be making plenty to overwhelm the smaller allies.
Turn 4 = Italy = Try to expand in the Middle East or Africa. With no US threat, Italy should be able to expand.
If all this works right, the US will be taken out of the picture and the other Allies should be much easier to deal with. Russia will go after Germany and may have some success at first. However Germany will have a huge amount of money to spend on lots of units to throw at the Red Army. Eastern US is worth 20 plus there is the plunder of the US treasury, which should be around 75-80 IPCs since Japan brought them into war the round before.
I imagine your allied players probably won’t want to continue this game.