People study international politics (i.e. international relations). Other people study international law. These people, in the past hundred years, stopped working with each other. Because the world is so much more connected now, regional politics and international law keep clashing. This is something that could be studied and/or fixed by people who study IP and people who study IL. Therefore, they cannot continue acting as they do (i.e. their behavior is no longer tenable), and they must start working together again.