@Azimuth
Politics are fine in the game, its just that this is a bit of a weird situation in the base game. Where some countries are linked but both can declare war.
Basically UK-Pacific breaks the rules by declaring war after their turn iso at the start of the turn.
If you want to work with politics its easy to make it stable.
There are only 2 ways to go from neutral -> War.
A : you declare war, after the start of the turn but before movement.
B : your enemy declares war on you.
As long as you follow those 2 rules you cannot generate weird situations.
This way you cannot start with enemy warships in the same SZ because either they attacked you on their turn and well 1 side doesnt survive, or you are still neutral at the start of the turn so they are not hostile.
And since loading of transports is checked at the start of the turn not start of the move your safe.