MICHAEL O’HANLON is a Senior Fellow and Director of Research at the Brookings Institu-
tion’s Foreign Policy Program and the author of The Senkaku Paradox: Risking Great Power
War Over Small Stakes (Brookings Institution Press, 2019), from which this essay is adapted.
September/October 2019 193
Can America Still Protect
Its Allies?
How to Make Deterrence Work
Michael O’Hanlon
S
ince the end o World War II, U.S. strategic thinking has been
dominated by the doctrine o deterrence. At its most simple, deter-
rence refers to one state’s ability to use threats to convince another
that the costs o some action—say, invading one o its neighbors—will
outweigh the bene¿ts. Such was the logic behind the Cold War concept
o mutual assured destruction: i either the United States or the Soviet
Union used nuclear weapons, the other would respond with nuclear
strikes o its own, resulting in the total devastation o both. By making
the costs o 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 o alliances that today
forms an essential part o the global order, the United States developed
a strategy o “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 o £¬¡¢. The point was not only to discourage Soviet adventurism
in Asia and Europe but also to reassure U.S. allies. I Germany and Ja-
pan (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 o extended deter-
rence remains central to the United States’ global power. Washington
is still, on paper at least, committed to using military (and, i neces-
sary, even nuclear) force to protect its allies from aggression by rivals.
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