The greatest risk facing the twenty-first-century United States, short of an outright nuclear attack, is a two-front war involving its strongest military rivals, China and Russia. Such a conflict would entail a scale of national effort and risk unseen in generations, effectively pitting America against the resources of nearly half of the Eurasian landmass.

The greatest risk facing the twenty-first-century United States, short of an outright nuclear attack, is a two-front war involving its strongest military rivals, China and Russia. Such a conflict would entail a scale of national effort and risk unseen in generations, effectively pitting America against the resources of nearly half of the Eurasian landmass. It would stretch and likely exceed the current capabilities of the U.S. military, requiring great sacrifices of the American people with far-reaching consequences for U.S. influence, alliances, and prosperity. Should it escalate into a nuclear confrontation, it could possibly even imperil the country’s very existence.

Given these high stakes, avoiding a two-front war with China and Russia must rank among the foremost objectives of contemporary U.S. grand strategy. Yet the United States has been slow to comprehend this danger, let alone the implications it holds for U.S. policy. So far, Washington’s efforts to grapple with the “simultaneity” problem (as it’s called in Pentagon circles) have been overwhelmingly focused on the military side of the problem. The 2018 National Defense Strategy (NDS) replaced the two-war standard with a laser focus on fighting one major war with America’s most capable adversary—China. In its wake, a debate has erupted among defense intellectuals about how to handle a second-front contingency.

By comparison, there has been much less discussion of how, if at all, U.S. diplomacy should evolve to avert two-front war and, more broadly, alleviate the pressures of strategic simultaneity. While the Trump administration rightly inaugurated a more confrontational approach toward China, this was not accompanied by a rebalancing of diplomatic priorities and resources in other regions to complement the NDS’ justified focus on the Indo-Pacific. Nor does the Biden administration appear to be contemplating a redistribution of strategic focus and resources among regions. This misalignment in the objects of U.S. military and diplomatic power is neither desirable nor sustainable. America will have to limit the number of active rivalries requiring major U.S. military attention, improve the functionality of its existing alliances for offsetting the pressures of simultaneity, or significantly grow defense budgets—or some combination of the three.

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