@loki17:
In Alpha 3+ when Japan is not at war with the British, can they fly over British territories?
Yes, and they have been able to in all iterations of the rules as well.
1. A power that is not neutral is free to fly over other territories with aircraft.
2. Japan begins at war with China.
3. UK/Anzac begin at war with Germany & Italy (even on the pacific boards, as only Russia has board specific neutrality).
4. Neither Japan or UK are neutral, therefore both can fly over each other’s territories.
The exception to the rules is that the UK or Anzac are not permitted to enter Chinese territories as a condition of their relations with Japan. Doing so requires a declaration of war on Japan by UK/ANZAC prior to movement into China, even for flyovers.