Debate over Donald Trump’s apparent interest in taking over Greenland from Denmark has exposed a serious weakness within NATO. While diplomacy may yet prevail, the situation highlights how dependent European allies have become on American military power. Decades of reliance on the USA have left the alliance vulnerable if Washington ever withdraws support or acts independently. The UK illustrates this clearly. Despite presenting itself as Europe’s strongest military force, Britain relies heavily on the United States, particularly through its nuclear partnership and key battlefield 'enablers' such as satellite intelligence, electronic warfare protection and logistics. Successive governments have underinvested in these costly capabilities, assuming American backing would always be guaranteed. This dependence extends across NATO. Many members operate US-built equipment and plan defence around American leadership. Even as allies try to do more, the alliance still assumes a dominant US role. The Greenland debate sharpens a question NATO already faces: what if America is no longer fully on board?