Russia’s invasion of Ukraine looks increasingly likely to lead to Finland and Sweden applying to join Nato. But whereas Helsinki appears to be doing so with something resembling gusto, Stockholm is inching towards the western military alliance more reluctantly.

As early as December and January, Finnish politicians started a national debate across party lines on how to improve their country’s security given Russia’s sabre-rattling then unprovoked attack on a non-Nato neighbour. The result is likely to be an overwhelming majority in Finland’s parliament in the coming weeks in favour of applying.

By contrast, Sweden’s centre-left government, itself deeply divided on Nato, initially appeared to hope it could dismiss the question of membership. It only started to take it seriously in recent weeks as Finland indicated it was likely to join regardless of what Sweden did, robbing Stockholm of its sole credible alternative: a defence alliance with Helsinki.

The main reason for the differing approaches, experts say, lies in the two countries’ reasons for staying away from Nato up till now and the basis for their longtime neutrality. Finland had its neutrality imposed on it as a way of dealing with the Soviet Union and their shared 1,340km border during the cold war. But for Sweden, neutrality has long been part of its national DNA, giving it an enviable record of not being involved in a conflict for more than 200 years.

“In Sweden, it is an identity issue. Due to the 200-year history of being non-aligned, it sticks in people as a normal thing. Finland has had a dramatic, and sometimes terribly difficult, situation,” says Gunilla Herolf, senior associate research fellow at the Swedish Institute of International Affairs.

Jarmo Lindberg, the former head of Finland’s defence, adds simply: “Finns are pragmatic. For Swedes, it’s more ideological.”

Geography also plays a role. Finland has a longer border with Russia than Nato in its current form, making the Nordic country acutely aware of the security threat. But for Sweden, with no border with Russia, Finland has historically acted as its buffer zone. The dark joke in Helsinki is that Swedes have for centuries fought their wars to the last Finn.

The differences are apparent in the way each country is moving towards Nato. When Finland’s parliament began discussing potential membership on Wednesday, the mantra across the political spectrum was on how to improve the country’s security. Faced with a Russia that is far more aggressive and unpredictable than Finns had hoped, there is a strong feeling that only Nato’s article 5 guarantee — whereby an attack on one is an attack on all — is strong enough.

But in Sweden the debate mostly revolves around the governing Social Democrat party. The four centre-right parties have been in favour of Nato membership for the past five years while the nationalist Sweden Democrats have said they would vote in favour if Finland decides to join the alliance.

That already gives a majority supporting membership in Sweden’s parliament. But the idea of entering the military alliance without the support of the Social Democrats — winner of every national election for the past century in Sweden — is close to unthinkable.

“It is very much part of the Social Democrat identity — it gave us a special space of manoeuvre in international politics in terms of mediation, peace talks and arms control. That’s the main explanation of why we’re acting so slowly now,” says Anna Wieslander, director for northern Europe at the Atlantic Council think-tank.

Things are now speeding up. The Social Democrats, who only confirmed their opposition to Nato in November, are debating whether to reverse their position with a decision due next month just as a hastily written government report on security policy will be released. The main Social Democrat newspaper, the tabloid Aftonbladet, last week altered its mind and declared its “reluctant” support for membership. Recent opinion polls show 58 per cent of Swedes in favour of joining and 21 per cent against. Most observers in Stockholm expect an application to come in tandem or just after Finland’s ahead of the Nato June summit in Madrid, albeit without passion.

“You don’t see any enthusiasm for this anywhere,” says Herolf. “You see some people saying it goes too quickly. And, of course, it does, but the security situation is as it is.”

richard.milne@ft.com; @rmilneNordic

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Nordics face Nato quandary if Trump is re-elected / From Thanos Papasavvas, London W1, UK