For seven decades, American power has been the invisible architecture holding Europe together. More than just its security guarantee under NATO, the U.S. military presence checked historic rivalries, subsidized collective defense, and created the conditions for unprecedented peace and prosperity.
During the Cold War, that guarantee meant Europeans could focus on cooperation among themselves and with America rather than on nationalist conflagrations. And the U.S. guarantee largely survived the end of the Cold War. Western European powers such as Belgium, Germany, Italy, and Spain took full advantage, devoting barely 1% of their GDPs to defense while investing in generous social programs.
The Trump administration is changing these dynamics. Its recent push to take Greenland from its NATO ally, Denmark, has heightened European anxieties and calls for decoupling from the United States. Still, the story of Europe’s quest for an autonomous defense capability is long and troubled.
Almost every major postwar initiative failed: the 1948 Brussels Treaty, the 1950s European Defense Community, Charles de Gaulle’s 1962 Fouchet Plan. At the 1998 Saint-Malo summit, the United Kingdom and France agreed to create “a European military force capable of autonomous action,” but progress has been near non-existent. The EU still lacks a unified, combat-capable army. Most members continue to rely on NATO, and in practice on the U.S., for tangible military power.
But what happens if American power continues to withdraw from the continent?
War. Without American power, Russia will test Europe. Russia already greatly outproduces European arms manufacturing. Absent American military consolidation, the Europeans will be tempted to accommodate Moscow. Russian power will grow and with it, a Chinese-led international order.
The second casualty will be European unity itself. The post-Second World War security order was built explicitly to tame German power and European nationalism. Yet, with the right-wing Alternative for Germany now the second-largest party in Parliament, the French right-wing National Rally party in a good position to challenge for the presidency in 2027, and the U.K.’s hard-right Reform party leading in opinion polls, we can see where Europe might be headed. Namely, to a future in which old hatreds may trump newer modes of cooperation. If Germany starts massive rearmament in the face of Russia’s threat, the French, Polish, and British will do the same.
The mistrust between Eastern and Western Europe runs deep. For 45 years, Eastern Europeans lived under Soviet occupation while Western Europe prospered under American protection. After the Cold War ended, Western Europe accommodated Moscow by becoming dependent on Russian gas and refusing to allow Georgia and Ukraine to join NATO. The consequence is that, from Warsaw to the Baltics, Eastern Europeans believe Western Europe can never serve as a reliable security guarantor. Think about it: If Russia used a tactical nuclear weapon against Polish forces or a small Polish city, would France really risk Paris and Lyon by retaliating against Russia with its own nuclear weapons? Would any British prime minister risk London or Manchester?
This understanding will accelerate fragmentation and an intra-European arms race. Perhaps the EU could prevent this competitive rearmament through more coordinated, cooperative defense. But historic fears are regenerating their political power.
We should not underestimate the influence America has brought to bear in tempering European disputes. Today, the U.K. and Spain still contest Gibraltar. Greece and Turkey remain at each other’s throats over Mediterranean gas fields and Cyprus. Bulgaria and North Macedonia have clashed over language. Hungary claims Romanian territory in Transylvania while cultivating ties with Moscow. Kosovo’s statehood remains contested, and Bosnian ethnic divisions simmer. Without American guarantees, these rivalries risk returning to the forefront, turning allies into competitors and potentially even adversaries.
The temptation of nationalist independence is always brewing in Europe. Even at the zenith of American power in the 1960s, Washington struggled to contain Charles de Gaulle’s pursuit of French strategic autonomy. Despite facing the Soviet threat and depending on American nuclear protection, de Gaulle withdrew France from NATO’s integrated command in 1966, expelled U.S. forces, and built an independent nuclear arsenal. With American withdrawal from Europe, similar calculations will drive decision-making across the entire continent.
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Washington should thus be wary. Trump may believe he can withdraw from Europe to focus on Asia, but European wars have a way of expanding beyond European borders. The U.S. needs a unified Europe, and Europe needs the U.S. in Europe. The U.S. should, of course, demand that the Europeans shoulder more defense burdens. But it should also recognize the substantial benefits for mutual peace, prosperity, and freedom that this alliance has brought to both sides of the Atlantic.
Whatever form it might take, the alternative will be far worse.