Secretary of State Mike Pompeo’s South China Sea statement on Monday is significant for two reasons: It shifts formal U.S. policy and it establishes a quiet jus ad bellum legal foundation for the use of military force against China in these waters.

Let’s start with the shift in U.S. policy. When the United States had previously condemned Chinese claims in the South China Sea, it had also called for regional negotiation to establish territorial ownership rights. This statement endorses a different approach, actively rejecting Chinese claims outright.