[@Little Bird] What we could do, if you really wanted to, is this: If you wanted to spend P to subvert an invasion, I would demand a sacrifice of all your P. If you had over 50 P, I would demand half. And the invader would be repelled for three rounds before they would be able to invade again.

Nope, no investment would be needed, but the one who is stolen from loses their goods, and the kidnapper/wealth stealer gets to see their efforts added to their 'wallet'.