@techroll42:
Actually, IIRC, there’s a helluva good reason: Mongolia. IIRC Mongolia doesn’t convert if USSR declares war.
Nope. Only if Russia attacks a Japanese controlled territory bordering Mongolia before Japan does the same. That means Manchuria almost specifically, but also addresses if Russia were to attempt to liberate Japanese held Chinese territories adjacent to Mongolia. Note that Japan is free to attack chinese territories occupied by Russian soldiers and that will result in no penalty, as they are chinese (not russia) territories.
There’s absolutely nothing that penalizes either for a state of war between them. It’s better for Japan if the US can’t land bombers in Russia and if the reds don’t reinforce china or india, but there’s NOTHING that prevents Russia from declaring war R1 and freeing movement for themselves (and their allies) on the pac board.
Soviet/Japanese Non Aggression Pact: Due to their mutual border conflct with Japan in 1939, the Soviet Union and Mongolia have a special relationship. If the Japanese attack any Soviet territory that is adjacent to any Mongolian territory, all Mongolian territories (Olgiy, Dzavhan, Tsagaan-Olom, Central Mongolia, Ulaanbaatar, and Buyant-Uhaa) that are still neutral are placed under the control of the Soviet Union at the end of the Japanese Combat Move phase, in the same manner as though the Soviet Union had moved land units into a friendly neutral territory. These territories have Soviet control markers placed on them, and their standing army units are placed on the board and are controlled by the Soviet Union player from then on. This occurs regardless of the state of relations between the Soviet Union and Japan at the time of the attack, with one exception: If the Soviet Union attacks any Japanese-controlled territory bordering these Mongolian territories while Mongolia is still neutral, Mongolia will remain neutral and not ally itself with the Soviet Union. In addition, the Mongolian territories will never become pro-Axis unless one or more of them is attacked by the Soviet Union.
Attacking is different from declaring war. Japan and Russia are free to declare war on each other without ever attacking each other at any time, over the entire length of the game.