@aaFiendish:
What round does this usually happen for you? I am curious if you are saying that is is round 2, or round 5. Since you say after three combined attacks, I would assume that it would have to be at the earliest round 6, assuming a complete pullback to moscow by russia, the quickest you could really reach moscow would be round 3. I think the sentiment of ignoring the UK and the USA is a good one, especially in plain 2nd edition.
Usually, the assaults on Russia proper start in round 4 and finish in round 5. Round 1 Germany has to re-take Eastern. Round 2, they assault (and sometimes take but cannot hold) Karelia. Round 3 they take and hold Karelia. All this time they are doing a heavy INF build with a few tanks to keep assault strength up. Also, if Russia stripped the Caucuses to defend Karelia, take it using the Med navy if it still exists in either round 2 or round 3; if Russia re-takes it, that simply weakens Moscow, if they don’t, it is extra land units for round 4). Meanwhile, Japan re-takes Manchuria in round 1 (if they still hold Manchuria on J1, subtract 1 from all that follows, and slap the Russian player around for bad gaming :-) Round 2 they take Yakut (and Soviet East Asia), round 3 they take Novosibirsk. Generally, both Japan and Germany have bombed Russia in round 3 also.
So in Round 4, Russia has very few IPC’s left (average is enough for 4 INF, 6 if they still hold Caucuses and bombing was poor). Germany throws EVERYTHING against Russia, even letting the UK or US have Western Europe if they took it in round 3. Bomber on ground support, remaining fighters, every ground force that can reach. They lose. More tanks and infantry are built in Karelia, and more land forces are moved up from Eastern. NOTE: If the Allies are played well, Germany will be securing Karelia this round instead of attacking Russia,
Japan follows up with another strike (or launches the first assault if Germany had to take Karelia this round). Usually 2-3 fighters, the bomber, a couple of tanks, and a few infantry; in short everything that can reach. If Germany assaulted Russia earlier in the round, suicide all airpower to kill as many INF as possible. If Germany did not assault Russia in round 4, save your air power… Move more land forces forward.
Round 5 Germany hits with everything in a VERY weak Russia (they only built 3 or at most 4 INF this round). If Germany was able to attack Russia in round 4, Russia falls. If not, Germany is now spent of offensive power (no air force, navy probably gone, one or 2 tanks at most) and is building INF to stave off the US and UK as they attack Germany proper. Allies may now hold both Eastern and Western Europe. The good news is they are building 10 or 11 units a round.
Later in round 5, if Germany did not take Russia earlier, Japan takes it with air forces to spare (but very few ground forces).
If Germany took Russia, they then build land forces for a couple of turns to kick the allies out of all of Europe, then air power to start whittling at the allied Navy. If Japan took Russia, they may need to build some tanks in Russia to assist in kicking the allies out of Europe.
Once Europe is re-secured, you either have an economic victory, or you start a war of attrition on the US and UK that will take quite a few turns while Japan sets up massive transport fleets in the Pacific, and Germany builds up enough air power (fighters work best since they also help defend against ongoing invasions) to blast the allied fleet around Britain, then a slow Naval build up in the Med, out of reach of UK airpower, to invade London (unless Japan is already there via Washington).
My win rate with this strategy is 100% vs. any of the AI opponents, and 70% with human opponents. Some games it takes a round longer, but that is rare (bad dice from time to time). On those human opponent games when it fails, is usually because of a combination of less than average dice, a significant technology hit by the US (heavy bombers especially) or an EXTREMELY aggressive US (not going to give away secrets here, it is a cruel strategy of non-intervention for 3 rounds, then two coordinated attacks on opposite sides of the world at just the right place). And to be honest, I have NOT found a counter to this non-intervention strategy as yet.