@knp7765:
So, if Japan and USA were at war, but USA did NOT declare war on Germany or Italy, you are saying it would be okay for US planes to land in London? Or for British units to be on US territories?
Yes.
@knp7765:
I’m pretty sure that the USA has to be at war on that side for that to happen.
Not true. Only Russia has split neutrality. Once any other player power is at war in one theatre, any neutrality rules are lifted. In point of fact, the only player powers that have neutrality rules placed on them are the US and Russia. The UK starts at war with Germany, even in the Pacific theatre, and does not act as a neutral power would on that side of the board, even if Japan does not provoke them. This is part of the reason that the UK can immediately move into FIC or the Dutch colonies. It’s also why British & Anzac planes can overfly Japanese territories and vice versa (as Japan is at war with China) prior to hostilitiies between Japan/Commonwealth.
@knp7765:
Of course, if Germany attacked London then they would be attacking those US units which is an automatic declaration of war by Germany on the USA.
Germany would need to officially declare war on the US before being allowed to attack any territory with US units in it. It’s a formality, but it’s not automatic. And as that’s prior to a combat move, that declaration is necessary to determine any movement blocks.