One of President Donald Trump’s chief complaints about America’s European allies is that they don’t spend nearly enough on defense; he has again raised the issue on Wednesday at the nato summit. Granted, Trump is hardly the first American president to point to miserly military spending on the part of fellow nato member states. This has been a sore spot in transatlantic relations since at least the 1970s. But the vociferousness of his complaints, and his transactional approach to alliances writ large, appears to have had an effect all the same. European powers are thinking harder about how to build their military strength and how they might use it in concert, even in—especially in—cases where the United States won’t be there to lend a hand.

In his seminal 2002 essay “Power and Weakness,” Robert Kagan, the esteemed foreign-policy analyst, warned of a widening transatlantic divide over the exercise of military power. Whereas Europeans saw themselves “moving beyond power into a self-contained world of laws and rules and transnational negotiation and cooperation,” Americans saw the world through a darker lens, in which “international laws and rules are unreliable and where true security and the defense and promotion of a liberal order still depend on the possession and use of military might.” In short, “on major strategic and international questions today, Americans are from Mars and Europeans are from Venus.” And that is why it was the United States that was always dragging a reluctant Europe into policing conflicts.

Now, however, we are on the cusp of a reversal. Americans, on the populist right, the socialist left, and most points in between, have lost their appetite for armed intervention, and the country’s chief conflict in the coming decades is likely to be a protracted cold war with an increasingly powerful Beijing. Europe, meanwhile, has no choice but to look southward, to the fragile states of Africa, which hold the key to its future. As Trump forces Europe to think about a future in which it provides for its own security needs, he may be pushing it toward a more Martian future, in which it is European militaries that go abroad in search of monsters to destroy.

Just last month, nine of Europe’s nato members declared their intention to work together on a “European Intervention Initiative,” or “EI2,” that is being championed by French President Emanuel Macron. Since the start of his presidency, Macron has been touting the idea of a pan-European security force capable of intervening in crises in North Africa and the Sahel, and it appears to be inching closer to reality.

To get there, though, Europe would first have to invest heavily in building its capabilities, as Sven Biscop, writing in Foreign Affairs, explains: “The main gap between the European and American arsenals has to do with strategic enablers—tools and resources such as intelligence and surveillance, transport, and precision-guided munitions, which allow countries to project military force safely and swiftly.” Without these strategic enablers, European strategic autonomy, as envisioned in Macron’s EI2, is but a mirage. For now, it is the United States that provides these strategic enablers to its allies, and that can always choose not to provide them. If Europe is to truly share in the burden of ensuring global security, it will have to pool its resources and replicate some of America’s existing capabilities. In short, the training wheels will have to come off.

The Trump administration, schizophrenic as ever, is both urging European nato allies to boost their military spending while condemning their tentative efforts to build up their own Europe-wide strategic enablers. Biscop attributes American wariness towards European strategic autonomy to a straightforward domestic consideration: fear that European governments will favor European defense contractors over their U.S. counterparts. But this underscores the deeper question: Does America really want a more independent and capable Europe? If it does, well, U.S. defense contractors might have to take it on the chin. Moreover, the United States must accept that such a Europe could, at some point in the distant future, serve as a check on American power, a prospect that some Europeans will relish and that many Americans will dread.

A more likely outcome, to my mind, is that a more autonomous Europe will devote itself almost exclusively to Africa. A decade or so from now, I suspect it is the European powers that will find themselves mired in armed conflicts, peacekeeping missions, and state-building efforts in the world’s most volatile regions, and the United States that will, regrettably, be standing aloof. Europeans will spend more on defense not in response to hectoring from Trump or his successors. Rather, they will do so out of necessity. The European Intervention Initiative, conceived in the wake of France’s military operations in Mali, is a sign of things to come.

Between 2010 and 2050, the working-age population of sub-Saharan Africa will grow from half a billion to more than 1.3 billion. That booming young population could be channeled into productive work at home, or, failing that, could seek it elsewhere. If current patterns persist, the economists Gordon Hanson and Craig McIntosh anticipate that the number of African migrants residing outside the continent will almost triple over this period, growing from 4.6 million to 13.4 million, and that most will settle in an aging Europe. Civil wars, climate change, and other looming calamities could spur emigration well beyond these projections.

Already, European states are devoting a growing share of their budgets to controlling migration, with a special focus on forging partnerships with African states willing to establish migrant processing centers on their territory, such as war-torn Libya. Their deeper challenge, however, lies in ensuring that African states have the institutional capacity they need to foster economic opportunity at home. Even ambitious migration advocates, such as Gerald Knaus of the European Stability Initiative, envision relatively modest annual inflows of African workers, perhaps in deference to the increasingly restrictionist sensibilities of the European public. At a time when the anti-immigration Alternative for Germany commands roughly as much public support as Germany’s storied Social Democratic Party, if not slightly more, talk of drastically ramping up immigration seems delusional.

Yet the alternatives to opening Europe’s borders will be daunting in their own right. Last year, researchers at the Center for Global Development released a working paper on the prospects for manufacturing in Africa, and their findings were sobering. With the important exception of Ethiopia, they found that industrial labor costs in most African states were far higher than one would expect when judging by their overall level of development. The upshot is that while export-oriented manufacturing has greatly reduced poverty in much of East Asia, Ethiopia might be the only country in sub-Saharan Africa suited to that development path. Other African states will have to make use of their labor abundance in other ways—for example, by developing their tourism sectors and by transforming themselves into destinations for wealthy expatriates. In other words, either Africans will come to Europe in search of employment, and Europeans will remake their societies to accommodate them, or Europeans will come to thriving African states in search of a higher quality of life, fueling the expansion of the local service-sector workforce in the process.

Unlike the 19th-century scramble for Africa, in which imperialists carved up the continent for their own purposes, this 21st-century infusion of European capital would have to be a cooperative venture, with African policymakers and entrepreneurs taking the lead. What they’d have in common, however, is that the question of security would be ever present: The European Intervention Initiative would be there to undergird the European Investment Initiative. New alliances and new rivalries would emerge. A rising Ethiopia, which is projected to have a population of 191 million in 2050, might eventually become as central to European security as a declining Russia, the population of which is expected to shrink to 133 million, is today.

As for the United States, expect it to concern itself more with Chinese and Indian power than with managing the stresses and strains associated with Africa’s demographic expansion. While Europe projects power in Africa, the U.S. will endeavor to preserve its relevance in East and South Asia, the new center of gravity of the global economy. And as the security interests of the U.S. and Europe diverge in the coming decades, perhaps Europeans will remember the Trump presidency as the moment they began to forge a more independent future.