Sovereign states have a responsibility not only to protect their own citizens, but also to protect— within their own territory—the rights and fundamental security interests of other states. Many states around the world, however, lack the resources to do so. Unable to exercise effective territorial control, these weak states frequently become safe havens for terrorist networks and other irregular groups. Yet the lack of such control is not the only reason for the existence of safe havens around the world; in some cases, the problem is not the host state's inability, but rather its unwillingness, to prevent irregular activity on its territory. The present article analyzes the challenges posed to the jus ad bellum resulting from both types of safe-haven scenarios: states that are unable, and those that are unwilling, to exercise control.