If you’re near a New York City subway stop, I can come over and show you some things to do. It’s always better to show these things in practice.
Otherwise -
The key is to stall with UK and USSR, until the US can come in and beat the Axis down.
If you’re going to go KGF, first, you make sure that Germany can’t really invade London successfully (if Germany buys a lotta transports, or has fighters in range of London - don’t forget, the fighters have to LAND too), then you buy a few infantry.
Otherwise, you buy UK and US navy and air until you kill the German fleet, while you use USSR to trade off territory with Germany. You withdraw the Allied forces in the east. If Germany has taken Anglo-Egypt on Germany’s first turn, you recapture it. (Germany will probably try to nab Africa, so you have to try to get it back quick; you can unite the Allied fleet off Algeria but watch out for German fighters from W. Europe plus any German navy that can blow up your fleet).
You get two fleets of US transports, and use one fleet to move units from E. Canada to London (you march the units from Washington to E. Canada), then you use the other transport fleet to move units from London to Europe. (It’s called a transport chain).
That’s KGF
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For KJF, just build a crapload of air and navy in the Pacific, and go beat up Japan.