This week, Secretary of Defense Pete Hegseth advised Asian nations that they must begin spending more on defense. We have heard a version of this before, most notably in the admonitions directed at our NATO allies. But the logic remains curious: are we truly safer when more countries mobilize?
The case for rearmament is not difficult to understand. NATO’s defenders would argue that peace in Europe was preserved precisely because aggression carried unacceptable costs. Deterrence, in this view, does not prevent war by eliminating weapons but by making their use irrational. The Cold War remained cold not because the major powers trusted one another, but because they feared the consequences of direct conflict.
Russia’s invasion of Ukraine shattered the assumption that large-scale conventional war in Europe was a relic of the past. Many believed that nuclear weapons had rendered such conflicts unthinkable. Moscow, of course, imagined a two-day operation, not a grinding war. But the lesson remains: what we consider unthinkable is often only untested.
For years, the United States urged NATO members to “pay up,” to spend more on defense. In a century scarred by tens of millions of deaths, such exhortations feel different. We had allowed ourselves to believe that the great age of mobilization was behind us. If peace was durable, then surely resources could be directed toward healthcare, renewable energy, education—anything other than weapons.
Perhaps that was naïve. Perhaps the arc of history bends toward justice only in textbooks. The end of the Cold War and the fading memory of the world wars encouraged a belief that we had learned something permanent. But history rarely grants permanent lessons. It grants only temporary reprieves.
And even if we have learned, others may not share our conclusions. Some states have interests that point toward a different vision of the world—one in which power is asserted rather than balanced, and in which military force remains a tool of national ambition. Their desire for armament does not make them right, but it does make them real.
Yet deterrence contains its own paradox. Nations rarely describe their own military buildup as threatening. They describe it as prudent, defensive, and necessary. The problem is that neighboring states often hear something different. One country’s insurance policy becomes another country’s warning signal.
History suggests that wars are not always caused by weakness. Sometimes they emerge from fear. States arm because they feel insecure. Their neighbors respond for the same reason. Before long, each side sees its own actions as defensive and the other’s as aggressive.
The question, then, is not whether nations should defend themselves. Of course they should.
The question is whether we have become too certain that more weapons necessarily produce more peace.
The decades following the Second World War were shaped by a different aspiration. Great powers would compete, but they would avoid direct confrontation whenever possible. The objective was not conquest but restraint. The Cold War was dangerous, yet much of its diplomacy revolved around preventing rival powers from colliding openly.
Today that assumption appears less secure. Russia has invaded Ukraine. Military solutions have become increasingly attractive in parts of the Middle East. And even in the United States, one occasionally hears discussion of Greenland, the Panama Canal, or Cuba in terms that would have sounded unusual to many postwar statesmen.
History offers evidence for deterrence.
It also offers evidence for arms races, miscalculation, and wars that began because governments mistook preparation for stability.
The danger is not merely that nations may be insufficiently armed.
It is that they may all conclude, at the same time, that safety lies in arming more heavily than their neighbors.
History suggests that this belief has produced both peace and catastrophe.