War is in the air: figuratively and literally. Even before the air strikes in Syria and the Russian veto of U.N. Security Council Resolution condemning Syrian use of chemical weapons, President Trump’s unpredictable and combative approach to foreign policy suggested a variety of paths which could lead to armed conflict with Iran, China, Russia or North Korea as Niall Ferguson, Robert Kagan, and Fareed Zakaria have all argued. In the post-World War II period, international law helped generate conditions which led to interstate peace—the “long peace.” Syrian airstrikes have, however, put unprecedented stress on the U.N. Charter-based international legal system regulating the use of force. Perhaps the result will be a more nuanced and better international legal system, one which is carefully calibrated to permit the use of force in response to humanitarian atrocities, as argued by Harold Koh and Rebecca Ingber. But perhaps degradation of the U.N. Charter-based limitations will weaken the international law prohibitions on the use of force, making regional or global conflict with China, North Korea, and Russia more likely. Those proposing an erosion of the U.N. Charter system need to consider carefully whether the international legal system is strong enough to make nuanced use-of-force distinctions. The answer depends in part on politics.

Viewed through a political lens, the prospects for a nuanced and effective international legal prohibition on the use of force look dim. Relaxing the prohibition on the use of force is likely to embolden the territorial ambitions of Russia and China; it will undermine the strength of the U.N. Security Council; and it is especially difficult to administer in a world of fake news and hair-trigger decision-making. The Syrian atrocities cry out for a response, but now is a dangerous time to tinker with the U.N. Charter’s prohibition on the use of force.

It bears emphasizing that for almost a century, the prevention of interstate conflict has been the core objective of international law. The League of Nations, established in the aftermath of World War II was designed to manage great power politics but failed to prevent World War II. That failure was shared by the 1928 Kellogg-Briand pact which outlawed war for the first time. After World War II, the victorious powers created the U.N. Charter and the Security Council with its permanent veto-wielding members: China, France, Russia, United Kingdom, United States. Note the continuing importance of those five powers. The Charter ushered in a remarkable “Long Peace”—meaning a dramatic reduction in inter-state armed conflict. The cornerstone of the U.N. Charter and of the international legal order since 1945 is a prohibition on use of force except in self-defense or as authorized by the Security Council. The “Long Peace” suggests that it has worked: not to prevent all conflicts, but to prevent many inter-state conflicts, which is the type of conflict building now.

Using the Syrian airstrikes to craft a humanitarian exception to the prohibition on the use of force puts the “Long Peace” under unprecedented stress. To be sure, the 1999 NATO bombing of Kosovo for humanitarian purposes violated Article 2(4) of the U.N. Charter. But the Syrian airstrikes, which involved the U.S. acting alone and without exhausting the avenues for peaceful resolution of the issue, represents a significant expansion of the Kosovo precedent, as analyzed by Ashley Deeks here.

There are several reasons to think that a limited and fine-tuned humanitarian exception to the prohibition on the use of force will not work. First, it will embolden the already emboldened territorial aspirations of Russia and China. After the bombing campaign and with the strong support of Western European countries and the United States, Kosovo declared its independence from Serbia in 2008. Serbia and its allies, especially Russia, strongly condemned the declaration of independence and continue today to refuse to recognize Kosovo. Russian officials, then, in turn used the Kosovo precedent to support its use of force in both Georgia and Ukraine. Crimea, which was part of Ukraine, is today Russian. The core threat to peace with Russia is probably—Syria notwithstanding—the increasingly militarized borders between NATO (or NATO-allied) countries and Russia, which includes thousands of NATO troops, the most since the end of the Cold War. The South China Sea is probably the world’s leading conflict-prone area—China’s territorial ambitions there may explain its uncharacteristic reluctance to criticize U.S. airstrikes in Syria. These political facts should give pause to those who seek a carefully-calibrated prohibition on the use of force.

Second, Syrian airstrikes undermine the United Nations Security Council, which did not authorize them, either ex ante or ex post. But the Security Council is a key forum for resolving other threats to interstate peace, such as Iran and North Korea. China, which is widely viewed as the key to containing North Korea, has recently highlighted its participation in developing the U.N. Security Council Resolutions designed to deter North Korean nuclear and missile programs. After all, international law provides the basis for imposing sanctions on North Korea to limit its nuclear ambitions. International law serves core North Korean objectives, too, as it prevents Western military intervention, a fear motivating North Korean policy. The Syrian precedent gives North Korea reason to worry that the U.S. will attack even over a Chinese veto in the Security Council. As with North Korea, international law strongly supports U.S. policy objectives of preventing a nuclear-armed Iran. Sanctions imposed by the United Nations Security Council led to the 2015 Joint Comprehensive Plan of Action, which relaxed sanctions in return for Iranian concessions on its nuclear program. Undermining the U.N. Security Council makes peace more difficult to achieve in this context, too.

Third, President Trump’s destabilizing leadership is the immediate cause of many dire scenarios forecasting war; such leadership makes exceptions to Article 2(4) especially dangerous and especially difficult to limit. President Trump’s use of force in Syria illustrates how hard it is to categorize such interventions as “one-off” incidents (on this point, see the exchange between Monica Hakimi and Anthea Roberts over at EJIL:Talk!) or to define their precedential impact in narrow terms. The very factors that were supposed to limit the Kosovo precedent, including the participation of a regional security organization such as NATO, failed to constrain the primary architect of those very limitations: the United States itself. A nuanced and fine-tuned set of factors justifying the use of force is hard to administer in a world of trigger-happy, truth-challenged leaders.