Some time back I played a game as the axis and there ended up being a strange predicament just before I would have achieved victory. Japan and Russia made their nonaggression pact so that a state of war could never exist between them (we were playing A 3.5). The turn before Japan took Calcutta for their 6th VC (with almost no way that any of their VCs could be taken back) the Russian player pulled a slick move and flew a fighter from mainland Russia to Calcutta to stop any takeover possibility. After much debate I persuaded the Russian player that because he could not be at war on the Pacific side of the map he could not move to Calcutta and I ended up winning.
Since that day I have spent much time wondering what would happen if Japan wanted to attack a territory like a U.K. controlled Persia containing a Russian unit, if Japan and Russia made the same nonaggression pact so that a state of war could never exist between them. I keep thinking that Japan should not be held back from attacking that territory just because of a Russian unit, so maybe Japan could just attack the U.K. units, but then what happens to the Russian unit if Japan takes control of the territory? Does the Russian get destroyed because it is in an illegal territory? Does it get a chance to move out on its next turn? Or can it just stay in a Japanese territory? The way I look at it is like a sea battle, if Japan attacks a sea zone containing units from U.K. and Russia without declaring war on Russia. Japan enters a hostile sea zone kills all of the U.K. units in that sea zone and that sea zone is now friendly for Japan. Russia is not forced out in this battle like I think that they should be in a land battle but you get the idea.
I would appreciate any thought or answers as to what to do if anything like this was to ever happen again.