Is there life after empire? I pondered the question last week at the Engelsberg Seminar, a gathering of academics, journalists and policymakers held in a disused ironworks two hours by car from Stockholm. Sweden once controlled vast stretches of northern Europe. It then contented itself, after a series of military defeats, to a more modest existence as a small neutral power with a healthy welfare state.

Judging from the quantity and quality of champagne consumed at Engelsberg, life after empire can be pretty sweet — so long as some other superpower can keep your world from falling apart. For generations, a nominally neutral Sweden could thrive only by aligning itself quietly, if unmistakably, with the American empire. Today, the country’s push for NATO membership is making that alignment explicit.

Sweden was once a mighty empire. During the 17th century, it was the leading Protestant power in continental Europe. After the Thirty Years’ War, it controlled much of Scandinavia and the Baltic region, as well as territories wrested from the Holy Roman Empire.

Decline set in only decades later. A disastrous defeat at the hands of Peter the Great — whom the Russian ruler President Vladimir Putin now emulates — at the Battle of Poltava in 1709 set off a long imperial retrenchment that eventually left Sweden as it is today. During the 20th century, Sweden was often seen — and saw itself — as the quintessential neutral state, one that sat out the world wars and the Cold War so that it could tend its own garden instead.

It has been a pretty nice existence. Sweden boasts the world’s 20th-highest per capita income. It pairs a robust capitalist economy with generous social welfare provisions. The country is famous for high levels of social capital and domestic cohesion, which enabled a remarkably light-touch approach to managing the COVID-19 pandemic, with day-to-day life continuing largely as usual. Corruption and crime are low, even though the latter is rising.

Sweden has done great, despite no longer being a great power. Which is perhaps why most Swedes seem not to miss the old empire much.

Yet Sweden’s story isn’t quite as simple as it might seem. Neutrality could be very profitable: The country infuriated the British during World War II by selling critical commodities to both sides. Yet that neutrality could also be precarious, as when the government felt compelled to let German troops cross Swedish territory on their way to attacking the Soviet Union.

And that stance could hardly have saved Sweden had Nazi Germany won the war and established its mastery over Europe. Adolf Hitler, who had little regard for the rights of smaller states, would not have left that country alone for a minute longer than he found convenient. The Swedish balancing act was only possible so long as the most aggressive, brutal states did not gain a preponderance of power.

Sweden tacitly recognized as much during the Cold War, when it was neutral in theory but never in practice. The country developed deep intelligence cooperation with the U.S. and NATO; it allowed Western forces to quietly use Swedish facilities and developed a high degree of interoperability with them. Sweden even reportedly enjoyed loose security guarantees — an “invisible alliance,” as one journalist later put it — from Washington and NATO.

A vulnerable Sweden would have faced existential danger in a world where the Soviet Union was ascendant, which is why Stockholm reconciled itself, if only informally, to American hegemony.

Today, Sweden is abandoning the last vestiges of neutrality in applying (along with Finland) to join NATO. But as officials in Stockholm told me, the reason Sweden can so easily be fast-tracked for membership — assuming a diplomatic dispute with Turkey is resolved — is that it has been such a close cousin of the alliance for years. The move into NATO may be a bold leap away from Sweden’s self-image as a neutral power, but it is a small step in view of the longer-running realities of cooperation with the alliance.

Sweden brings real military heft, from its high-quality air combat and undersea warfare capabilities to its vital strategic geography in the Baltic. And the country has good, specific reasons to take this step. The Defense Ministry is worried about Russian designs on strategically situated Gotland Island, as well as ongoing Russian encroachments in Swedish waters, airspace and cyberspace.

These concerns, of course, have been amplified by the invasion of Ukraine, showing that a country lacking formal security guarantees is guaranteed nothing — and that the stability of the international system that allowed Sweden to thrive is no longer assured.

Sweden’s NATO bid thus represents an open recognition of something its leaders have long understood: Small and medium countries can only succeed in a world where the balance of power is held by those who would protect their freedom rather than those who would destroy it. The Swedish empire is long gone. Fortunately for Sweden, the American empire isn’t.

Bloomberg Opinion columnist Hal Brands is the Henry Kissinger Distinguished Professor at Johns Hopkins University’s School of Advanced International Studies and co-author of “Danger Zone: The Coming Conflict with China.”