@WILD:
Japan relied very heavily on resources from mainland Asia, and oil from the E Indies etc. That’s the reason it wanted to expand. Your not just cutting off its allies, your cutting off its ability to wage war through its own means as well. The same would go for UK, w/o resources from it’s own Commonwealth (and the US), it couldn’t have kept its factories going. Germany had all of Europe to plunder its resources, but still relied on shipping for iron ore and other raw materials.
All good points. The convoy rules, like many things in A&A, are a bit abstracted. Rather than trace convoy routes on the map that would create clutter and confusion, a decision was made that convoy raids would be done at the termini of convoys - where they started and ended. Raiding the sea zone around Japan represents hitting convoys coming in from places like China and the East Indies, as well as intracoastal shipping. Even within a single territory (say, from Osaka to Tokyo), it’s often cheaper and more efficient to move supplies by ship than over land.