Was Trump’s threat to end Iran’s civilization a war crime?

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In the wake of U.S. President Donald Trump’s threat on social media to destroy an entire civilization ahead of a fragile Iran ceasefire, legal experts are questioning whether such incendiary language can amount to a war crime — even if it is never carried out.

Just hours before a Tuesday night deadline tied to U.S. demands on Tehran, Trump wrote on Truth Social that “a whole civilization will die tonight, never to be brought back again.” A ceasefire announced Wednesday between the U.S., Israel and Iran has since paused further strikes, though its durability remains uncertain.

For Stephen Rapp — a former U.S. ambassador-at-large for war crimes issues who prosecuted Liberian ex-leader Charles Taylor, who was ultimately convicted of war crimes and crimes against humanity — the answer is direct.

“My view is yes,” Rapp told POLITICO, pointing to Article 51 of Additional Protocol I to the Geneva Conventions, which prohibits threats intended to terrorize civilian populations.

In his view, the law does not require the violence to happen. “Even if the threat isn’t fulfilled, it’s still a crime,” he said. “If I threaten to kill your children, but don’t follow through, it’s still the kind of extortion the law recognizes.”

The White House, in response, framed Trump’s comments in terms of domestic authority rather than international law.

“President Trump’s preference is always diplomacy,” White House spokesperson Anna Kelly said, adding that he will use his “constitutional and lawful authorities” to protect the U.S.

The episode has sharpened a legal question rarely tested so starkly: Can a threat alone — even one delivered in a social media post — constitute a war crime?

It is not the first time such concerns have surfaced. Threats of strikes against civilian infrastructure during the conflict, including directed toward power plants and desalination facilities, have already drawn accusations of potential war crimes. It underscores how Trump’s language has shifted the focus from conduct alone, to rhetoric as well.

Can threats be war crimes?

This principle, Rapp argued, has already been tested in court.

“That sort of threat against a civilian population — that kind of intimidation — is prosecutable,” Rapp said, citing precedents including the International Criminal Tribunal for the former Yugoslavia’s Prosecutor v. Stanislav Galić case over the 1990s siege of Sarajevo, and the Special Court for Sierra Leone’s conviction of Charles Taylor. “It is, under international law, a war crime in and of itself.”

Not all experts go that far, even if they agree Trump’s statement crosses a legal line.

Kevin Jon Heller, a professor of international law at the University of Copenhagen, described the post as “a clear violation of Art. 2(4) of the U.N. Charter,” which prohibits the threat or use of force against the territorial integrity or political independence of another state.

“Nothing in the U.N. Charter, not even the right of self-defense, justifies destroying an entire country because you don’t like its government,” he told POLITICO.

He also pointed to the laws of war, which prohibit “acts or threats of violence the primary purpose of which is to spread terror among the civilian population.”

“There seems to be little doubt that spreading terror among Iranian civilians is the primary purpose of Trump’s threat,” Heller noted. “That said, Trump’s threat is unlikely to qualify as a war crime,” he added, noting that international tribunals have typically required such threats to result in “grave consequences” for civilians — and “that has obviously not happened yet.”

Others suggest such rhetoric may be unlawful under international law without necessarily meeting the threshold for a war crime.

“These threats violate the prohibition against giving no quarter,” said Gerry Simpson, professor of public international law at the London School of Economics, referring to a rule in the laws of war, codified in Additional Protocol I to the Geneva Conventions, that forbids declaring that no enemy fighters will be spared or that surrender will not be accepted.

“This is obviously cruel and dangerous — and possibly deranged,” Simpson told POLITICO. “But it also constitutes an act under international law and one with legal effect.”

At the heart of the debate is a distinction that international law draws, sometimes awkwardly, between what is unlawful and what is criminal.

International law clearly prohibits threats of force, including under the U.N. Charter’s ban on “the threat or use of force” against other states. But turning such threats into war crimes typically requires a higher bar, with international tribunals focusing on conduct that produces concrete effects, as reflected in case law from tribunals such as the International Criminal Tribunal for the former Yugoslavia’s Prosecutor v. Dragomir Milošević.

The American legal lens

Any assessment of Trump’s statement, however, is shaped by a deeper and long-standing tension: how the U.S. itself approaches international law.

Washington has historically taken a selective approach to international legal commitments. While it has adopted parts of the Geneva framework, the U.S. has not ratified Additional Protocol I — the provision Rapp cites — meaning it is not binding under U.S. law.

The U.S. is also not a party to the International Criminal Court and has repeatedly challenged the authority of international tribunals over American officials, including by sanctioning ICC judges and prosecutors over investigations into alleged war crimes by U.S. personnel in Afghanistan and, more recently, Israeli conduct in Gaza.

Successive administrations have maintained that U.S. courts — not international ones — should determine the legality of U.S. conduct, a position reflected in Washington’s long-standing rejection of ICC jurisdiction over its nationals.

That position reflects a cornerstone of the American legal system: that international law binds the U.S. primarily where it has explicitly consented, and that domestic law ultimately prevails.

John Yoo, a law professor at the University of California, Berkeley, who served in the Justice Department’s Office of Legal Counsel during the George W. Bush administration, said that hierarchy is built into the U.S. constitutional system.

“The United States is a nation which, under its constitution, domestic law comes first and international law second — and only if it is enacted by the correct lawmaking processes,” Yoo told POLITICO. “Otherwise it is a policy decision for the president to decide whether the nation will follow an international law rule.”

Yoo added that the U.S. has “created and enforced the international rules-based system since 1945,” describing that as “the truly exceptional aspect of American primacy.”

Others frame the issue less as a question of legal hierarchy and more as one of how the U.S. applies international law in practice.

“The U.S. stands out because it historically has aggressively demanded that other countries comply with international law while excepting itself from key provisions and treaties,” Eric Posner, a professor at the University of Chicago Law School, told POLITICO.

“To be sure, other countries are also selective in their approach to international legal commitments,” he added.

That approach is reflected in how the White House frames Trump’s remarks, as it emphasizes U.S. security interests over international legal constraints.

“Iran can never be allowed to threaten the security of the United States by possessing a nuclear weapon,” White House spokesperson Anna Kelly said.