One of the virtues of a good theory is that it makes sense of events that might otherwise seem surprising or at least somewhat puzzling. A case in point is the Swedish and Finnish decision to abandon long traditions of neutrality and apply for membership in Nato.
At first glance, the explanation for this decision seems blindingly obvious. Russia started the most destructive war in Europe since World War II and has waged that war with considerable brutality. As the war in Ukraine drags on and threatens to become a destructive stalemate, Sweden and Finland have concluded that their security environment is deteriorating and have opted for the greater protection that they believe Nato membership will provide. If you studied international relations in college, you might see this as a classic example of balance-of-power theory at work.
Still, that explanation leaves a couple of questions unanswered. Abandoning a long and successful policy of neutrality is a big step, and it could involve significant costs and risks down the road. This point is especially pertinent in the case of Sweden, which has cooperated closely with Nato for years and was already getting many of the benefits of membership with few of the burdens. So why change course now?
More importantly, one might have thought that Russia's abysmal military performance in Ukraine would have left Sweden and Finland feeling more rather than less secure. The war has shown that Russia's armed forces are simply not very good at conquering other nations, and the combination of Western sanctions, the costs of the war itself, and the continuing brain drain of talented young Russians even as the overall population declines and ages is going to reduce the country's power potential for years to come.
When one remembers that Sweden remained neutral throughout the Cold War, when Soviet power was at its height, it is at least somewhat puzzling that Sweden (and Finland) picked this moment to decide they needed Nato's embrace.
As I've argued for a long time now, puzzles such as these disappear if we recognise that traditional balance-of-power theory is incomplete. States do pay close attention to the balance of power, but what they really care about are threats. The level of threat a state poses to others is partly a function of its overall power, but also its specific military capabilities (especially its ability to conquer or harm others), its geographic proximity, and its perceived intentions.
Generally, states that are close by are more dangerous than those that are far away. Similarly, states with armies that are optimised for conquest look more dangerous than states whose forces are designed primarily to defend their home territory. And states that seem content with the status quo tend to induce less alarm than states that seem bent on revising it.
Balance-of-threat theory explains why Iraq's seizure of Kuwait in 1990 led to the creation of a balancing coalition whose combined capabilities dwarfed Iraq's economic foundation and third-rate military. It also explains why Europe has responded so vigorously to Russia's invasion of Ukraine but has taken only modest steps to respond to the rising power of faraway China. China is much stronger than Russia and likely to be a greater long-term challenge, but it is on the other side of Eurasia and lacks military capabilities that can plausibly threaten Europe itself.
In the case of Sweden and Finland, the tipping point was clearly an altered view of Russian intentions. As Swedish Prime Minister Magdalena Andersson told reporters over the weekend, Sweden decided to apply to join Nato because it has changed its views on Russia's willingness "to use violence" and "to take enormous risks."
Notice that Russia's motivations for invading Ukraine aren't the central issue for the Swedes—it doesn't matter if Russian President Vladimir Putin is a dyed-in-the-wool expansionist or driven largely by a profound sense of insecurity. What matters is that he chose to go to war.
The Swedish and Finnish reaction (and the reaction of the West in general) tells you a lot about how states perceive and respond to threats. In general, states have more trouble figuring out how to react to countries whose power is increasing due to their own internal efforts, but who are not (yet) using that power to alter the status quo or trying to become stronger by taking territory from other states.
There are exceptions to this tendency: The United States got away with expanding across North America and dismembering Mexico in the 19th century because it was separated from the other major powers by an enormous ocean, and the European states remained focused on each other and not on the upstart Americans. But so long as rising states don't start throwing their weight around, others are likely to try to profit from their growing wealth and do relatively little to contain them.
They may cast a watchful eye on a rising power, but the reaction will be muted until there is evidence that it is willing to use its power directly. That's why China's earlier strategy of a "peaceful rise" was so successful, and why Chinese leader Xi Jinping's more assertive actions have provoked increased concern.
Whatever you think Putin's motivations are, it is now abundantly clear that he miscalculated badly and on several levels. He underestimated Ukrainian nationalism, and he exaggerated Russia's military capabilities. Like other unsuccessful aggressors, he also failed to understand a key lesson of foreign-policy realism: States balance against threats. And using force to revise the status quo is just about the most threatening thing that a country can do.
War is sometimes necessary, and every now and then a war will pay off handsomely for the country that started it. But launching a war invariably alarms other states, and it usually brings them together to contain the danger. Putin may have believed Europe was too divided and dependent on Russian oil and gas to oppose his action, so he gambled that he could accomplish his aims quickly and eventually get back to business as usual. What he got instead was classic realist balancing behaviour, driven by a revised assessment of Russian intentions. Overwrought denunciations of supposed Ukrainian Nazis and the brutal behaviour of Russia's soldiers just made the Swedish and Finnish decisions easier.
Is this all that is going on in Stockholm and Helsinki? Probably not. Nato's ability to rapidly supply Ukraine with advanced armaments—an undeniably impressive display of logistical prowess—may have made membership look more valuable. Russia's failure to escalate in the face of mounting Western support for Ukraine—at least so far—may have also allayed Swedish and Finnish concerns about possible Russian countermeasures. Seeing Russia as simultaneously weaker and more belligerent may have made abandoning strict neutrality look like a safer option.
Whatever the reason, there is a broader lesson that more world leaders ought to take to heart: States are sensitive to power, but they're even more sensitive to the ways that power is used. If you have a big stick, speaking softly is smart. So is using one's power wisely—and not very often.
Stephen M Walt is a columnist at Foreign Policy and the Robert and Renée Belfer professor of international relations at Harvard University.
Disclaimer: This article first appeared on Foreign Policy, and is published by special syndication arrangement.