Zachary Miller, Staff Member
Since his election, President Trump has engaged in a war of words with North Korea’s “supreme leader,” Kim Jong-un. Trump has promised “fire and fury,” and threatened to “totally destroy” North Korea should war erupt. But under what circumstances would war with the DPRK be legal?
The use of military force is subject to both domestic and international law. The U.S. Constitution gives Congress, not the President, the power to declare war and provide funding for the military. Trump is therefore limited in the types of actions he can undertake without Congressional approval. The President can still use military force during “a national emergency created by attack upon the United States,”  though the President must report such actions to Congress within 48 hours and cannot unilaterally extend such actions beyond sixty days.
Internationally, the use of force is far more constrained. Under the U.N. Charter, force beyond self-defense must be authorized via a U.N. Security Council Resolution in response to a “threat to the peace, breach of the peace, or act of aggression.” The U.N. Security Council has only done this twice in its history — during the Korean War, and during the First Gulf War. A new UNSC Resolution authorizing force against North Korea would have to overcome the veto power of the permanent members on the Security Council.
Self-defense, then, is perhaps the only legal justification available for a hypothetical war against the DPRK. However, it is not a legal carte blanche to effect regime change. The defense of one’s soldiers or state must be proportional to the threat. Unhelpfully, it is unclear what is supposed to be proportional to the threat — the wartime conduct of the defending state, the war goals of the defending state, or both. The limits and boundaries of this doctrine are elusive.
The United States has repeatedly stated that it will not allow the DPRK to acquire intercontinental ballistic missiles (ICBMs) capable of reaching American soil. Should North Korea acquire such weapons, the U.S. might undertake a pre-emptive defensive strike. To comply with international law, the military action would have to satisfy the three elements of the Caroline test, articulated by Secretary of State Daniel Webster in 1837. To show pre-emptive self-defense, he argued that a state would have to show that the “necessity of self-defense was instant, overwhelming, leaving no choice of means and no moment of deliberation.” This test would make it impossible for the U.S. to plan a pre-emptive war of self-defense — any ability to deliberate the war would foreclose a justification of pre-emptive self-defense.
International law tightly curtails unilateral decisions to use force. There are very few scenarios in which war against North Korea would be legal. This conflicts with the views of most adult Americans, 58% of whom support military action against North Korea if the U.S. could not peacefully accomplish its goals there. Meanwhile, 59% of adult South Koreans oppose pre-emptive U.S. military strikes against North Korea. Lacking unanimous support from the American and South Korean peoples, the legality of a war with North Korea will continue to be a pressing topic for academics and politicians.
 Peter Baker & Choe Sang-Hun, Trump Threatens ‘Fire and Fury’ Against North Korea if It Endangers U.S., New York Times (Aug. 8, 2017) https://www.nytimes.com/2017/08/08/world/asia/north-korea-un-sanctions-nuclear-missile-united-nations.html.
 Ali Vitali, Trump Threatens to ‘Totally Destroy’ North Korea in First U.N. Speech, NBC News (Sep. 21, 2017 8:01 AM ET) https://www.nbcnews.com/politics/white-house/trump-un-north-korean-leader-suicide-mission-n802596.
 Ryan Vogel, Commentary: Would War with North Korea Be Legal?, Salt Lake Tribune (Aug. 8, 2017) http://www.sltrib.com/opinion/commentary/2017/08/08/commentary-would-war-with-north-korea-be-legal/.
 U.S. Const. art. I, § 8, cls. 11–12.
 Youngstown Sheet & Tube Co. v. Sawyer, 343 U.S. 579, 637 (1952) (Jackson, J., concurring) (“When the President takes measures incompatible with the expressed or implied will of Congress, his power is at its lowest ebb, for then he can rely on upon his own constitutional powers minus any constitutional powers of Congress over the matter.”)
 War Powers Resolution, § 2, 50 U.S.C. § 1541(c) (2012).
 Id. at § 1543(a).
 Id. at § 1544(b).
 U.N. Charter art. 39.
 S.C. Res. 83 (June 27, 1950).
 S.C. Res. 678, ⁋ 2 (Nov. 29, 1990)
 David Kretzmer, The Inherent Right to Self-Defense and Proportionality in Ius Ad Bellum, 24 Eur. J. Int’l L. 235 (2013).
 Donald Trump (@realDonaldTrump), Twitter (Jan. 2, 2017 3:05 PM), https://twitter.com/realDonaldTrump/status/816057920223846400.
 Indeed, the United States has made such a strike a part of its National Security Strategy. See White House, The National Security Strategy of the United States of America 15 (Sept. 17, 2002) (“For centuries, international law recognized that nations need not suffer an attack before they can lawfully take action to defend themselves against forces that present an imminent danger of attack. We must adapt the concept of imminent threat to the capabilities and objectives of today’s adversaries.”)
 Frederic L. Kirgis, Pre-emptive Action to Forestall Terrorism, Am. Soc. Int’l L. (June 2002) https://www.asil.org/insights/volume/7/issue/8/pre-emptive-action-forestall-terrorism.
 U.S. Majority Backs Military Action vs. North Korea: Gallup Poll, Reuters, (Sep. 15, 2017 7:26 AM) https://www.reuters.com/article/us-northkorea-missiles-usa-poll/u-s-majority-backs-military-action-vs-north-korea-gallup-poll-idUSKCN1BQ1LP.
 Most South Koreans Doubt the North Will Start a War: Poll, Reuters (Sep. 8, 2017 12:35 AM) https://www.reuters.com/article/us-northkorea-missiles-southkorea-poll/most-south-koreans-doubt-the-north-will-start-a-war-poll-idUSKCN1BJ0HF.