And my point is it's not about a physical blockade. If you buy your ships from half way around the world, then the shipyards can be destroyed before you get an

And my point is it's not about a physical blockade. If you buy your ships from half way around the world, then the shipyards can be destroyed before you get anywhere near them. And certainly now preventing that is politically commiting to a war on the other side of the planet which may not immediately effect you, but is likely to eventually. But the other part is: you don't have to physically do anything. You could deny shipping to your opponent by someone just outbidding you for the output. Why not? You're already outsourcing so you're cost sensitive, and guaranteed volume is cat nip to manufacturers - no amount of strategic alliance wording is going to save you if an adversary reliably buys 10x as much.