@Captain:
So lets see if I have this straight. If Russia attacks any Japanese territory bordering Mongolia, Mongolia will not become allied so Japan can now move freely into Mongolia. If Japan attacks any territory boardering Mongolia, then Mongolia become allied. Is this only before all countries are at war with each other or does this stand as long Russia and Japan are not at war with each other? I’m still a little bit confused.
That’s close but not quite right. Assuming we’re talking 2e rules, then at the start of the game, a defense pact is in effect between Mongolia and the USSR. If Japan invades any originally-owned Russian territories that border Mongolia, then the Mongolian troops and territories become Russian. This is different than the normal procedure for activating neutrals.
If Russia attacks a Japanese-controlled territory adjacent to Mongolia or invades Korea, then this defense pact is vitiated and Mongolia is then treated as a strict neutral. So Japanese troops can’t move in without declaring war on all the true neutrals in toto. Personally I think this treaty does Russia more harm than good since Mongolia has no IPC value. If all of those territories suddenly become Russian, then Japan gets a huge path opened up into the Russian interior (the 6 INF are a bit too scattered to really help much).