we had warning of what was to come. Not that a warning about an impending act of aggression cures the act. A centerpiece of modern international law is that territory changes hands only by consent, never by force. The rule of territorial stability is more than just another rule of international law. It is the indispensable rule of our system of law between States, and to let it lapse will send us back to an age of disorder. However you look at it, it is evident that relations among states—and the system of law that states have built since 1945—will change fundamentally, if we dispense with that rule.