The White House has not ruled out the possibility that the United States could use force to take control of Greenland, an autonomous territory belonging to the Kingdom of Denmark.
Both Denmark and the United States are NATO member states, which makes this scenario particularly sensitive in terms of international security.
1- What would happen if one NATO country attacked another?
Such a situation is not foreseen by NATO. The alliance, founded in 1949, was built as a defense organization to guarantee the collective security of its member countries. Danish Prime Minister Mette Frederiksen has stated that “if the United States were to choose to attack another NATO country, then everything would end, including NATO itself and the security architecture that has been built since the end of World War II.”
2- Does the NATO founding treaty foresee an attack between allies?
No. The NATO Treaty does not provide for the possibility of one member state attacking another, nor for a procedure for the expulsion of a state. Article 1 of the Treaty states that the parties undertake, in accordance with the UN Charter, to settle any international disputes by peaceful means and to refrain from the threat or use of force in any manner inconsistent with the purposes of the United Nations.
3- What does Article 5 of NATO provide?
Article 5 is the foundation of the Atlantic Alliance. It stipulates that an “armed attack” against one or more member states in Europe or North America will be considered an attack against them all, activating collective defense. NATO’s supreme commander is always an American general, and the defense of Europe is closely integrated with that of North America.
4- Is the European pillar of NATO self-sufficient?
No. The main financial and military contribution to NATO comes from the United States. At the NATO summit held in The Hague last June, the 32 member countries committed, under pressure from US President Donald Trump, to increase defense spending to 5% of Gross Domestic Product by 2035. According to NATO estimates, US defense spending in 2025 amounted to about $980 billion, compared with 99 billion Danish kroner (about $15.5 billion).
5- Does the European Union provide for mutual protection between member states?
Of the 27 countries of the European Union, Austria, Ireland, Malta and Cyprus are not part of NATO. Article 42.7 of the Lisbon Treaty stipulates that, in the event of a military attack on an EU member state on its territory, other member states are obliged to provide aid and assistance.