For more than seven decades, Europe's security has relied entirely on a network of alliances centred on the United States. This structure - which has successfully withstood disagreements between allies and the end of the Cold War - has been experiencing a serious existential crisis since the White House became home to a president who finds it inconceivable to back a permanent commitment to defending Europe that might imperil the very existence of the United States. Europe thus finds itself asking some hard questions. In the face of world powers like China and Russia, it is obviously in Europe's interest to maintain the Atlantic Pact. Only if this were to prove impossible would Europe have to really think about European defence strategies without any alliance with the US. It has the material resources, but does it have the strategic culture needed to navigate this shift? One thing that is certain, however, is that given the strategic upheavals taking place, the force of inertia will not be enough.