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On January 7, 2025, President Trump said the United States needs Greenland and refused to rule out using military or economic pressure to take it. Denmark’s Prime Minister responded within hours, stating that Greenland will not be owned by the United States. The confrontation placed an 80-year-old rule at the center of global attention: you can’t take land by force anymore.
For eight decades, this prohibition has been the bedrock of global order. It theoretically prevents powerful countries from rolling tanks across borders and declaring their neighbors’ land to be theirs now.
The rule appears in the UN Charter’s Article 2(4). All member states “shall refrain in their relations from the threat or use of military action against a country’s land and right to govern itself.”
Trump’s threat raises a question. Does this rule mean anything when a superpower decides to ignore it?
The 1945 Prohibition on Conquest
Before World War II, conquest was how the world worked. A stronger country could defeat a weaker one, take its land, and that was that—legally recognized, accepted worldwide. The Concert of Europe didn’t try to prevent conquest. It managed the diplomatic fallout.
Japan invaded Manchuria in 1931. Italy took Ethiopia in 1935. Nazi Germany annexed Austria, then Czechoslovakia, then Poland. Each time, the aggressor claimed legitimate national interests. Each time, the community wrung its hands and did nothing, because law didn’t forbid conquest—it regulated how you went about it.
World War II’s carnage made that system untenable. The victorious powers—led by the United States—decided that permitting nations to acquire land through military action created an intolerable incentive structure. As long as military conquest remained a legal path to expansion, nations would keep building militaries large enough to conquer their neighbors. That meant perpetual war.
The UN Charter, signed June 26, 1945, prohibited conquest absolutely. Article 2(4) made the threat or use of military action against another state’s integrity a violation of law. Article 103 said that when Charter obligations conflict with any other treaty, the Charter wins.
This was a binding legal obligation, backed by Security Council enforcement powers including the authorization of military action to reverse violations.
Over the next twenty-five years, the prohibition became stronger and more widely accepted. The 1960 Declaration on Colonial Independence reframed questions around self-determination rather than conquest. The 1970 Declaration on Friendly Relations crystallized the consensus: forcible action that deprives peoples of self-determination violates law. Legal scholars classified this rule as jus cogens—a rule so fundamental that no state can violate or contract around it, like the prohibitions on slavery or genocide.
How Enforcement Works
The first real test came in August 1990, when Iraq invaded Kuwait and declared it Iraq’s 19th province. Saddam Hussein’s military overwhelmed Kuwait’s defenses in hours. If the community did nothing, the entire post-1945 legal structure would be revealed as meaningless.
The response was swift and overwhelming. The Security Council passed Resolution 660 condemning the invasion and demanding withdrawal. The Council then escalated through sanctions and naval interdiction. Ultimately, Resolution 678 authorized member states to “use all necessary means” to compel Iraq’s withdrawal. Borders were restored exactly where they’d been before the invasion.
The system worked because of Security Council consensus. All five permanent members either supported the action or abstained. No vetoes. That consensus made military enforcement possible.
Consider what happened in 2014, when Russia invaded and annexed Crimea.
Russia occupied the peninsula with unmarked military personnel and staged a referendum under military occupation on March 16, 2014. Russia then formally annexed the region. The UN General Assembly passed a resolution declaring the referendum invalid—100 nations in favor, only 11 opposing. The community imposed economic sanctions. The European Union, United States, Canada, and others coordinated restrictions on Russian access to capital markets and targeted Russian officials.
Russia maintained control of Crimea through 2022 and beyond, despite international condemnation. Sanctions imposed costs but couldn’t reverse the conquest. Russia has a permanent seat on the Security Council and could veto any enforcement action. No military coalition could be authorized. Economic pressure alone wasn’t enough.
The pattern repeated in February 2022 when Russia launched a full-scale invasion of Ukraine and annexed four additional Ukrainian regions. The ICC issued arrest warrants for Putin. Sanctions expanded. But Russia continued to occupy Ukrainian land, and the community had no enforcement mechanism that could compel withdrawal without military action directed at a nuclear power.
The rule works against countries without special UN power to block enforcement and nuclear weapons. It works imperfectly—or not at all—when permanent Council members are willing to endure sanctions and isolation.
Every nation acknowledges that conquest is illegal. Even Russia frames its actions as protecting ethnic minorities or responding to NATO expansion—arguments that implicitly acknowledge that conquest is illegal and must be justified through other claims. But the enforcement mechanism has a built-in exemption for great powers.
Trump’s Threat and NATO
What Trump said about the Arctic island represents something qualitatively new. Not because the United States hasn’t violated law before—it has, repeatedly. But because Trump is explicitly threatening to use military action to acquire land from a NATO ally, and he’s not bothering to offer legal justifications.
When asked whether he would rule out using military action to take the island, Trump refused. He suggested Copenhagen has failed to defend it adequately—claims Danish officials have categorically denied.
This rule wasn’t about preventing war between great powers alone. It was about dismantling the entire framework of colonial domination—the idea that powerful nations could simply take what they wanted from weaker ones.
Trump’s proposal violates NATO’s Article 5. NATO’s Article 5 says an attack on any member is an attack on everyone. If the United States militarily seized the Arctic island, it would constitute an armed attack on Copenhagen, theoretically obligating other NATO members to defend Denmark. The alliance would fracture. The post-1945 order would be revealed as unable to constrain even its architect.
The Enforcement Vacuum
If Trump tries to take the island by military action, the Security Council won’t authorize military action to stop it—the United States holds a veto. The world couldn’t impose sanctions on the U.S. like it did on Russia; the U.S. economy is too large and too central to global trade. NATO would split, with some members honoring their Article 5 commitments and others declining to fight the United States.
The likely response: diplomatic condemnation, General Assembly resolutions (which carry symbolic weight but no enforcement power), targeted economic pressure short of sanctions, and countries would shift their partnerships and allegiances as nations seek to build counterbalances to American power.
Brazil, China, Russia, and other nations would accelerate the formation of alternative institutions less dependent on American leadership. The UN system would be revealed as fundamentally incapable of constraining great power behavior. And the credibility of law would suffer catastrophic damage.
If the United States can acquire land by military action and keep it, then Russia’s claim to Crimea and eastern Ukraine becomes legally indistinguishable. China’s potential seizure of Taiwan or expansion in the South China Sea—where a tribunal already ruled China’s claims have no legal basis—would follow the same precedent. India and Pakistan could resolve Kashmir through military conquest. Every nation with military superiority over its neighbors would face constant temptation to use that superiority for expansion.
The post-1945 order depends on one key idea: whatever their power disparities, all states are bound by the same rules. The moment that assumption collapses, the framework designed to prevent war becomes aspirational rhetoric with no binding power.
Who Benefits From This Rule
Copenhagen, with 5.9 million people, can coexist with the United States only because law says the United States can’t take its land. Remove that, and Copenhagen’s security depends entirely on American goodwill—which is fundamentally different from the rule of law.
This is why Global South nations responded to Trump’s threats with such alarm. Colombia’s president denounced what he characterized as aggression directed at the sovereignty of Venezuela and of Latin America. Mexico’s president declared that America is not owned by any doctrine or force, emphasizing that the region’s sovereignty cannot be claimed by external powers.
If the United States can violate this standard, so can China, Russia, and every other power. It benefits all nations equally by establishing that military superiority doesn’t justify acquisition.
China benefits when this standard prevents Russian expansion into Central Asia. Russia benefits when it prevents NATO expansion or American military action. Every nation benefits from living in a world where all other nations are constrained by the same rules.
Only a nation that perceives itself as permanently militarily superior to all others would prefer a system where powerful states can acquire land by military action. And no nation occupies that position.
The Historical Irony
This standard wasn’t imposed on the United States by others. The United States created it.
The idea that land acquired by military action cannot be legally recognized was first articulated by U.S. Secretary of State Henry Stimson in 1931, in response to Japan’s invasion of Manchuria. The Stimson Doctrine—that the community should refuse to recognize changes achieved through military action—became foundational to post-war order precisely because the United States championed it.
The United States drafted the Charter. American diplomats negotiated Article 2(4). American military power enforced this standard when Iraq invaded Kuwait. For eighty years, the United States has claimed to be the defender of the rule-based order.
To have an American president now reject this represents not a violation of law alone but a repudiation of the American-led system that has governed relations since 1945.
Trump’s administration has signaled explicit skepticism about law’s relevance to American conduct. Trump has stated that it’s up to him to determine when the United States should comply with rules that bind others. In January 2025, he withdrew from the World Health Organization, the Paris Climate Agreement, and numerous other treaties. His administration has imposed sanctions on ICC officials who investigated American conduct.
These actions signal a fundamental challenge to the post-1945 order: the assertion that the United States, as a superpower, isn’t bound by the same rules that constrain other nations.
What Happens Next
Every nation acknowledges that conquest is illegal. Even violators attempt to justify their actions through legal arguments rather than openly asserting a right to take land by military action. The fact that even violators use legal arguments to justify their actions suggests the 1945 norm has achieved something more than paper significance. It’s embedded in global consciousness.
But enforcement directed at militarily powerful states remains fundamentally dependent on political will rather than legal mechanisms. Russia holds Crimea despite years of condemnation and sanctions. Russia occupies substantial portions of Ukraine despite overwhelming opposition and ICC arrest warrants. China expands its military footprint in the South China Sea despite tribunal rulings opposing its claims.
What Trump said about acquiring the Arctic island by military action represents the most severe test of this norm since 1945. If he attempts to follow through and succeeds, people will stop believing that international law matters. This standard will remain formally in place—the Charter won’t change—but it will have been revealed as unequally applicable: binding on weak states but not on superpowers.
Russia would cite American precedent to justify holding Ukrainian land. China would cite it to justify action directed at Taiwan or expanded claims in the South China Sea. Every nation with military superiority over its neighbors would face reduced constraints on using that superiority for expansion.
The alternative is that Trump backs down—recognizing that even the most powerful countries must follow the rule. That would demonstrate the 1945 legal order’s capacity to withstand challenges even from its most powerful member state.
The stakes extend far beyond the Arctic. They concern the foundation on which peace and security rest in the twenty-first century. The legal system created in 1945 is still in place. What hangs in balance is whether the most powerful state will choose to respect the framework it helped create—or whether we’re about to discover that eighty years of law has been, for great powers at least, more suggestion than constraint.
The prohibition has endured because it serves every nation’s interest in stability and predictability. Small nations gain protection from larger neighbors. Medium powers gain assurance that regional rivals cannot simply seize disputed territories. Even superpowers benefit from a system that channels competition into economic and diplomatic arenas rather than military conquest.
When the United States led the effort to create this framework in 1945, American leaders recognized that a world where military conquest remained legal would require permanent military mobilization, constant intervention to maintain balances of power, and recurring wars that would drain resources and lives. The prohibition served American interests by creating a more stable, predictable international environment.
A world where powerful nations can seize land from weaker ones is a world of constant military tension, arms races, and conflict. It’s a world where alliances shift rapidly, where economic development suffers from perpetual insecurity, and where nuclear-armed powers face constant temptation to use military superiority for territorial gain.
The prohibition prevents that world. It establishes that borders, however imperfect or historically contested, cannot be changed through military action. That principle has prevented countless wars by removing the primary incentive for military aggression: the prospect of territorial gain.
Trump’s willingness to challenge this principle represents either a fundamental misunderstanding of why the United States created it or a calculated decision that American interests are better served by a return to a world where military might determines territorial control. Either way, the challenge forces every nation to confront a question that has been settled for eighty years: Do we live in a world governed by law, or by power?
The answer will determine not only Greenland’s fate but the structure of international relations for decades to come. If the prohibition holds, the post-1945 order demonstrates its resilience. If it fails, we enter uncharted territory where the constraints that have prevented great power wars for eight decades no longer apply.
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