US can’t rely on ‘forces’ to deter China, Russia

If US troops were deployed on Taiwan, China’s government-run Global Times warned in August, Beijing would “destroy and expel” them and “realise reunification by force.” Two months later, media reports confirmed that the Pentagon had indeed placed small numbers of US forces on Taiwan. The People’s Liberation Army didn’t strike. But the episode was enough to make one wonder whether the US can rely on the presence of its own military personnel to discourage a Chinese assault.
It also raised broader questions about whether so-called tripwire deployments — forces too small to defeat a determined attacker — can still help deter aggression, in Taiwan or elsewhere. The answer is that tripwire forces can indeed signal American resolve to protect vulnerable territory. But they only have the desired effect if tied to a credible plan for what happens after the shooting starts.
The presence of roughly two dozen US special operators on Taiwan wasn’t entirely a secret, but it got global attention after the Wall Street Journal broke the story in October. Such a tiny contingent cannot prevent Beijing from conquering the island; its purpose is to train Taiwan’s ground forces and strengthen defense ties between Washington and Taipei.
Whether such deployments have deterrent value is something American strategists have debated since the early Cold War.
The flashpoint then was West Berlin, which hosted some 12,000 US and allied troops that had no hope of protecting a city surrounded by Soviet armies. What could those troops do? “Bluntly put, they can die,” the strategist Thomas Schelling wrote. “They can die heroically, dramatically, and in a manner that guarantees that the action would not stop there.”
He meant that once US troops were killed in West Berlin, American honor would be engaged, and a larger intervention would follow. A tripwire force could thus dissuade aggression on even an isolated, dangerous frontier.
The debate has flared again as great-power war has become more likely. Earlier this year, two leading political scientists
argued that token deployments don’t really deter, because the enemy can simply execute a fait accompli — a quick seizure of territory that leaves overmatched defenders no chance to respond.
Other analysts countered that tripwire forces put the fear of obliteration into aggressors by manifesting US commitment.
The debate isn’t simply academic. US policy makers need good ways of protecting strategic terrain in Taiwan, the Baltic region and the South China Sea. So they also need a nuanced understanding of what small deployments can achieve. History suggests that tripwire forces work best when they are strong enough to put up a decent fight and carry the plausible promise of something worse to come.
Consider again the Berlin scenario. America’s theory of deterrence was not that the Soviets would blanch
at killing 12,000 armed hostages. It was that this tripwire contingent was mighty enough to make Moscow use a lot of force if it attempted to conquer West Berlin, an aggression so egregious that it would trigger a more devastating war. That threat was realistic because the Berlin garrison was backed by a much larger allied presence in Western Europe, which had well-rehearsed plans for fighting the Red Army — and for using nuclear weapons if that resistance failed.
Now consider a different scenario. In June 1950, the US had several hundred troops in South Korea. But as the scholars Dan Reiter and Paul Poast note, they were insufficient to deter a North Korean invasion,
because Washington had given no indication that it could or would come to Seoul’s defense. President Harry Truman did ultimately decide to fight in Korea, waging a bloody war the US had could perhaps have averted with a stronger deterrent force.
Today, deploying more special operators to Taiwan, or adding permanently stationed US forces to the small North Atlantic Treaty Organization (Nato) presence in the Baltic countries, can help lessen any uncertainty about whether Washington would defend its friends against unprovoked attack. This kind of signaling is particularly valuable in Taiwan’s case, where the US is inhibited — by longstanding fears of Chinese sensitivities — from making ironclad defense commitments.
But these deployments won’t do much good by themselves. The presence of Ukrainian troops in Crimea didn’t deter Russia’s seizure of the peninsula in 2014, because those troops gave up rather than fight a war they would surely lose.
Likewise, if the US can’t actually defend Taiwan — by helping the island survive air and missile barrages, and flooding the region with naval and air power — then Beijing might think that an American tripwire is only a bluff.
Unless Nato can stop Russian forces from winning quickly in the Baltics, Moscow might conclude that token deployments are signs of weakness, not strength. And just sticking a few dozen US troops in an exposed position — such as on one of the defenseless offshore islands claimed by Taiwan — might be dangerous, because Beijing could subdue that force with small-scale aggression and then dare Washington to escalate wildly in
response.
The tripwire metaphor is apt: The idea is that breaking it leads to a large, deadly explosion. Small deployments can pack a big deterrent punch when they are part of a broader, credible defense strategy, but not when they are a substitute for it.

—Bloomberg

Hal Brands is a Bloomberg Opinion columnist, the Henry Kissinger
Distinguished Professor at Johns Hopkins University’s School of Advanced International Studies, and a scholar at the American Enterprise Institute. Most recently, he is the co-author of “The Lessons of Tragedy: Statecraft and World Order”