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President Donald Trump has refused to rule out using force to seize Greenland from Denmark. Not economic pressure. Not diplomatic isolation. Actual force against a NATO founding member that has been one of America’s closest allies for seventy-seven years.
What happens to NATO if the United States attacks Denmark?
The answer, according to Danish Prime Minister Mette Frederiksen, is straightforward. “Everything would come to an end,” she told Danish broadcasters. The international community as we know it. Democratic rules. NATO itself—the world’s strongest alliance—would collapse.
International Response and Contingency Planning
Speaking aboard Air Force One last Sunday, Trump made statements indicating a willingness to use force to acquire Greenland, telling reporters “if we don’t do it the easy way, we’re going to do it the hard way.” When reporters pressed him on whether that meant military action, he didn’t back down, stating “I’d love to make a deal with them. It’s easier. But one way or the other, we’re going to have Greenland.”
White House Press Secretary Karoline Leavitt added that “utilizing the U.S. armed forces is always an option at the Commander in Chief’s disposal.”
Denmark responded by announcing a $2 billion investment in Arctic defense capabilities. Seven European countries—France, Germany, Italy, Poland, Spain, the United Kingdom, and Denmark—issued a joint statement asserting that “Greenland belongs to its people.” Decisions about its future must be made exclusively by Greenlanders and the Danish government. Finland withdrew from the Ottawa Convention banning antipersonnel mines, citing changing security conditions.
Article 5 Creates an Impossible Situation
NATO’s core rule, Article 5, says that if any member is attacked in Europe or North America, that attack “shall be considered an attack against them all.” This mutual defense provision is the entire point of NATO—the guarantee that transformed independent nations into a genuine alliance.
If the United States attacked Denmark to seize Greenland, the Danish government would invoke Article 5. This would obligate all NATO members—including the United States itself—to treat the American attack as an attack on all NATO members requiring collective response.
The United States contributes roughly seventy percent of NATO’s expenditure and houses command infrastructure. As international law analysts have noted, there’s no realistic possibility for other alliance members to effectively challenge U.S. superiority.
So Article 5’s guarantee becomes meaningless precisely when it matters most. NATO would be trapped in an impossible situation: obligated to defend Denmark but practically unable to do so.
Rasmus Jarlov, chair of the Danish parliament’s defense committee, put it bluntly: “NATO would be finished. Then [the US] would have destroyed the most powerful, most successful alliance in history for no reason.”
International Law Violations
A U.S. attack on Denmark would break the UN’s fundamental rule against using force, which explicitly forbids “the threat or use of force against the territory or freedom to govern itself of any state.” Force is permitted only to defend yourself from attack or when authorized by the UN Security Council.
Greenland poses no threat to the United States. The UN Security Council would never authorize such action—France and the United Kingdom would veto it immediately, and Russia and China would oppose it.
The 1951 Defense Treaty on Greenland explicitly obligates the United States to respect Danish sovereignty over Greenland. An American attack would constitute a fundamental breach of this bilateral treaty.
Greenland’s status under international law provides additional protection. The Self-Government Act of 2009 officially recognized Greenlanders’ right to self-determination. Under international treaty law, any agreement reached under duress—through threat or use of force—wouldn’t be legally binding.
Even if the United States managed to compel Greenland through force to sign an agreement ceding sovereignty, that agreement would have no legal validity. The U.S. could occupy Greenland, but it couldn’t legally acquire it or establish legitimate sovereignty over it. International pressure and legal isolation would continue indefinitely.
The 1951 treaty also includes specific provisions for consultation and cooperation on defense matters. Any U.S. action that violated these consultation requirements would constitute breach of contract under international law, giving the Danish government grounds for legal action in international courts.
Congressional Authority and Constitutional Constraints
The Constitution gives Congress the power “to declare War.” No American president can legally wage war without either an explicit declaration of war by Congress or genuine self-defense against actual immediate danger. Denmark poses no imminent threat to the United States.
Congressional Democrats and Republicans have already made clear they would unite to prevent action. Senator Tim Kaine declared that “I think Congress will stop him, both Democrats and Republicans” and that “We’re not going to do it the hard way, and we’re not going to do it the easy way either.”
Congresswoman Maggie Goodlander, a naval intelligence officer and member of the House Armed Services Committee, stated: “Our Constitution entrusts Congress – not the President – with the power to declare war, and I will not stand idly by while the President attempts to send America’s sons and daughters into harm’s way for reasons that defy common sense.”
If Trump attempted to order action without authorization, congressional leadership would face immediate pressure to use the War Powers Act—a law that lets Congress stop military operations not authorized by Congress within sixty days.
Constitutional constraints only work if people enforce them. Trump has shown a consistent willingness to test the boundaries of executive authority. Congress might block action, but the fact that we’re discussing this possibility has already done enormous damage to the alliance.
Greenlandic Opposition
All five political parties in Greenland’s parliament issued a joint statement: “We don’t want to be Americans, we don’t want to be Danes, we want to be Greenlanders.”
This unified opposition from across Greenland’s entire political spectrum destroys any excuse the president might make about acting in Greenland’s interests or with local support. Prime Minister Jens-Frederik Nielsen emphasized that Greenland’s “future must be decided by the Greenlandic people,” and the collective statement expressed desire for the United States’ “contempt for our country” to end.
About fifty-six percent of Greenlanders would vote for independence in a referendum, though only if their standard of living could be maintained. The threats have mostly strengthened Greenlanders’ commitment to independence from both Denmark and the United States, seen as threats to Greenland’s independence. Nielsen stated that Greenland feels “sad” that the American president has “reduced our country to a question of security and power.”
If America took over Greenland, people would resist—a population of fifty-seven thousand who actively oppose American sovereignty. The occupying forces would need to suppress the native population’s aspirations for self-government. In a territory of fifty-seven thousand people, everyone knows everyone. Any occupation force would face unified resistance with deep local knowledge of terrain and conditions. The Arctic environment itself presents extraordinary logistical challenges that would multiply the costs of maintaining an unwelcome presence.
Strategic Rationale and Existing Arrangements
Trump argues that the United States “needs” Greenland “from the standpoint of national security” because Greenland’s current defenses amount to “two dog sleds” and Russian and Chinese “destroyers and submarines” patrol the waters around Greenland.
The problem with that argument: Trump claims he needs to seize Greenland to prevent Russian expansion in the Arctic, but the act of seizing Greenland would advance Russian strategic interests by undermining international law. Russia has consistently argued that Western nations are hypocritical about international law—claiming territorial sovereignty for themselves while violating it when convenient. American seizure of Greenland would prove Russia’s claim that the international system is based entirely on great power competition rather than principles. This would undermine America’s argument that Ukraine should keep its borders.
China could claim the same right to forcibly acquire territories it views as strategically necessary—Taiwan, portions of the South China Sea, disputed border regions with India. The notion that international law constrains great power behavior would be fatally undermined.
The United States already has substantial access to Greenland through the 1951 Defense Treaty and maintains Pituffik Space Base (formerly Thule Air Base) there. Denmark has signaled willingness to negotiate enhanced security cooperation. The U.S. could potentially gain much of what it claims to need—substantial infrastructure, exclusive access, participation in resource extraction—through negotiation without the catastrophic costs of action.
The existing Pituffik Space Base already provides the United States with radar systems for ballistic missile early warning, satellite tracking, and space surveillance. The base has operated continuously since 1951 under Danish sovereignty without significant problems. Trump told the New York Times that ownership of Greenland is important because “that’s what I feel is psychologically needed for success,” suggesting the motivation is presidential ego satisfaction rather than logical thinking about strategy.
Cascading Consequences
The most likely resolution involves increased American presence in Greenland through expanded agreements with Denmark, enhanced U.S. investment in mining infrastructure, and possibly expanded American participation in Greenlandic governance without formal annexation. Denmark has already signaled willingness to negotiate, and the 1951 Defense Treaty provides a framework.
But if Trump interprets continued resistance as justification for action, the consequences would be severe and potentially irreversible.
A U.S. attack on Denmark would trigger Article 5 meetings, leading to the most serious NATO crisis in the alliance’s history. Other NATO members would be forced to choose between supporting a response to American aggression or effectively abandoning the alliance’s mutual defense principle.
What would follow would likely include European independence initiatives, and countries would rethink their alliances. Asian allies would question whether to trust America, and Russia-China cooperation would strengthen. European diplomats told CBS News that Greenland rhetoric represents a potential “breaking point” in the transatlantic relationship and has caused them to fundamentally reassess American commitment to European security.
Europe’s reasoning is unavoidable: if the United States is willing to attack its most loyal allies to acquire territory, then American security guarantees are worthless. Denmark has been one of America’s most loyal allies, and lost more soldiers in Afghanistan than most NATO countries. If loyalty to the United States provides no protection from American aggression, what’s the point of alliance membership?
For Asia-Pacific allies like Japan, South Korea, and Australia, an American attack on Denmark would be equally alarming. These nations have structured their entire security strategies around the assumption that the United States would defend them from Chinese aggression. If the U.S. demonstrated willingness to attack a NATO ally, why should Asian-Pacific nations believe American security guarantees would constrain American behavior toward them?
Japan and South Korea might pursue independent nuclear weapons programs. Australia might reduce its security dependence on the United States. These cascading strategic consequences would tear apart the alliance system that the United States has maintained since 1945, leaving America dominant but strategically isolated.
The Path Forward
NATO’s whole idea is that members defend each other from common threats and that no member would threaten another. If that assumption no longer holds, NATO in its current form cannot survive.
Congress has signaled its determination to prevent action. The administration has indicated that negotiation remains the preferred path. Denmark has demonstrated willingness to enhance security cooperation through existing legal frameworks. European nations have unified in support of Danish sovereignty while remaining open to discussions about Arctic security.
The path forward leads toward working together using current agreements and institutions, greater investment in Arctic security by both the United States and its allies, and figuring out who gets minerals and access through negotiation rather than force.
The fact that such a path needs to be explicitly negotiated, rather than assumed, reflects how profoundly the rhetoric has damaged the trust that NATO needs to survive. Whether that damage can be repaired will become clear in the coming months.
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