I agree w/ColonelCarter
When you say “contain” I guess that you mean what resources you need to throw at one power to slow, or stop (maybe retard) expansion as you go hard after the other. As pointed out below Italy doesn’t really belong here, but they can be used to prop up German defenses, or take out blockers for their big bro. So I guess you are looking for how many turns the US would need to focus on one power to “contain” them (spend income for 2-3-4 turns or more) then switch gears to cripple the other.
Italy is by far the weakest especially if the bulk of their navy is taken out on the first turn. So they would be the easiest to contain because once the allies control the Med they can convoy them to near zero income w/o actually taking them out. So unless the Germans give them a lot of help they are the easiest to contain (no news here)
I think that Japan would be next on the list because again if you manage to take out the Imperial Navy, you can crack into the DEI and Asia which is a large part of their income source. Take away half their income and their empire will collapse. However with a J1 attack the Japanese navy will be very hard to put a dent into early in the game (depending on what they hit). By say the 5th turn Japan probably has most of SE Asia including DEI and most likely India. They will be in a defensive position at sea that because of the massive air power could go offensive so it will be an uphill battle for the Allies. So containing them (take out the fleet) will be very expensive and time consuming IMO. With that said though, the Japanese Empire is vast and much is over water, so it is difficult to protect it all. In the Pac the Anzac is the key. They need to build ships to def the combined allied navy, or possibly work as a clean up crew if/when the US gets the chance to attack or defend in a naval battle. The Anz also need to be ready to grab Japanese possessions or trade them when the US takes out blockers. Anz having subs ready to convoy can also be helpful too, even if you are just forcing the Japanese to trade destroyers for subs (how many DD’s do they have?). If the Japanese get greedy and splinter off part of the Imperial navy to push deeper into the Mid east or Africa they will have some weak spots.
I chose Germany (assuming no Sea Lion) as the most difficult to contain, mainly because they will push to Moscow regardless of what you do, and as time goes on will set-up def to use against allied landings. As the allies you will need to get some help (UK ftrs) to Moscow to cause a delay. With the newer bomber strat they are more difficult to crack. The Allies need to build more navy to get over which means fewer ground units for the landings. The Germans don’t necessarily need to take out the combo allied navy when they come over (very costly), they can position a few ground units in keys places to use with the over powering Luftwaffe to wipe out allied landings w/o taking much of a hit on the air force. The Germans with some navy (seems to be popular) and say 3 transports in the Baltic is part of that strat for def/reclaiming Norway if the allies blow the wad up there. So if the allies are going north, they will need to take out the German Baltic navy ASAP (if it exists).
Like I said above there are some things that the allies can do to stall the Germans when going after Moscow. Getting UK ftrs to Moscow for one, or ground units heading north from the Middle east. I also like to boost Russia’s income like having them take Iraq asap for the NO bonus (gives them 5 IPCs/turn) and getting the lend lease/no western units NO (until you land UK ftrs).
So my question back to you is if you are able to stall the Germans from taking Moscow for 2-3 or more turns, is this containing them lol?