Can America Still Protect Its Allies?

How to Make Deterrence Work

The deterrers: Polish forces at a NATO exercise in Poland, November 2018 Craig Ruttle / Redux

Since the end of World War II, U.S. strategic thinking has been dominated by the doctrine of deterrence. At its most simple, deterrence refers to one state’s ability to use threats to convince another that the costs of some action—say, invading one of its neighbors—will outweigh the benefits. Such was the logic behind the Cold War concept of mutual assured destruction: if either the United States or the Soviet Union used nuclear weapons, the other would respond with nuclear strikes of its own, resulting in the total devastation of both. By making the costs of war intolerably high, both sides hoped to keep the peace. 

Yet for Washington, deterrence was never merely about protecting the U.S. homeland. As it built the postwar system of alliances that today forms an essential part of the global order, the United States developed a strategy of “extended deterrence.” According to this strategy, the United States would use its military power, including its nuclear arsenal, to defend its treaty allies—among them Japan, South Korea, and the states of NATO. The point was not only to discourage Soviet adventurism in Asia and Europe but also to reassure U.S. allies. If Germany and Japan (to take just two examples) knew that Washington would guarantee their security, they would not need to take actions—such as building a nuclear bomb—that might destabilize the international system. 

Today, the Soviet threat is gone, but the strategy of extended deterrence remains central to the United States’ global power. Washington is still, on paper at least, committed to using military (and, if necessary, even nuclear) force to protect its allies from aggression by rivals. The stationing of U.S. military forces abroad gives additional credence to this commitment, as any attack on a major ally would likely cause U.S. casualties, all but guaranteeing a U.S. military response. Today, Washington’s two principal geopolitical rivals are China and Russia. China is a rising power

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