> there is the Mutual Defence Clause (article 42.7 of the Treaty [of Lisbon]

Article 42.7 “leaves more room for interpretation than one might expect for a clause in a legally binding text” [1].

If Finland and Sweden turned down NATO membership and then suffered territorial degradation, I doubt the U.S. would step in. That, in turn, might motivate EU members to exercise their opt outs or neutrality caveats, or find that all that can be done within their power is send non-lethal aid.

[1] https://ecfr.eu/publication/ambiguous-alliance-neutrality-op...

To expand on this: It also explicitly provides for an opt-out to preserve the neutrality of countries like Sweden and Ireland, such a clause being added at their insistence.

I suspect that when the rubber hits the road nothing would happen, are Western European countries going to get into a potential nuclear exchange with Russia defending an EU member that's got a carve-out allowing them not to do the same for them?

That doesn't apply for Finland in the same way, but I'd still expect more of a "thoughts and prayers" response from the EU than anything else.

1. https://ecfr.eu/article/commentary_article_427_an_explainer5...

Well, I'm pretty sure Europe is capable of sending nuclear missiles that would destroy any FOB Russia set in Finland (this wouldn't trigger Russia doctrine of only using nukes to defend its territory, not its troops).

Invasion would become way to costly for a demographically challenged country.

Would EU countries waste their nukes in attrition of RU troops on aligned soil? There aren't that many (by official figures). I'm guessing most countries would prefer not to escalate to nukes unless their own territory was threatened.

This is not how NATO works, and very likely not how the mutual defense clause works. Article 5 doesn't apply if you send your soldiers on some mission (e.g. defending Finland) on your own accord and Russia kills them. The EU clause is generally interpreted - from what I've read - to not require other EU members to offer direct military support to the attacked nation.

> Article 5 doesn't apply if you send your soldiers on some mission (e.g. defending Finland) on your own accord and Russia kills them.

That depends where you send them, as Article 5 has geographical constraints specified in Article 6 (there is no general exceptions for troops being attacked after being voluntarily sent “somewhere”.)

Moreover, even without triggering Article 5, an attack on NATO member troops in the Euro-Atlantic region but outside the territory specified in Article 6 would probably be a trigger for regional security consultations under Article 4, which have produced more NATO interventions than Article 5.

Just because the EU gets involved, doesn't mean NATO will follow suit.

There's an argument that EU is the aggressor for the purposes of Article 5 if it comes to the aid of a non-NATO member. The USA and other non-EU members would have the option to sit that one out, if they wanted. Alternatively, they could offer support to only NATO members.

This is probably part of what's spurring NATO membership. I bet most Fins and Swedes thought that the USA would deploy forces the event of a conflict. Now they see that American policy will be aid only, regardless of the death and destruction.

I have never heard of that being a common sentiment, or actually any Swede thinking that. Swedes have never assumed America will deploy troops.

> There's an argument that EU is the aggressor for the purposes of Article 5

There is no such thing as “an aggressor for purpose of Article 5“; and the only case to be made for an “aggressor” status that would obviate Article 5 commitments is an aggressor under international law (that is, someone engaging in aggressive war in violation of the UN Charter, North Atlantic Treaty, and customary international law.)

Participating in individual or mutual self-defense action outside the scope of NATO doesn't void Article 5 (we know, because it didn't, despite definitely being part of the scenario, in the only actual Article 5 invocation in history.)

Mutual defensive pacts are not transitive. Germany being in NATO does not mean that every country Germany has a defense pact with is de facto in NATO.

Finland probably doesn't want to find out the hard way how the USA is going to decide to roll here. Being a NATO member removes all doubt as to what happens.

The EU defense clause is no NATO replacement and in a state of war it is highly unclear would it even merit material transfers. Currently it's more of a gesture or suggestion for future collaboration.

Unfortunately, no, not by implication. Chapter 5 only means defending a country that's attacked. So if Russia invades Finland, and say France send troops to defend it, and Russia retaliates against France, then US, UK, and Turkey are not obliged to defend France. As far as NATO is concerned it's France's affair.

In reality of course the the non-EU NATO members will probably decide to get involved one way or the other, but they are not legally bound to it.

> Chapter 5 only means defending a country that's attacked.

This is true, but there are no limitations on the circumstances of the attack. For instance, if the US was fighting a low-grade global war with an Afghanistan-based terrorist network that has not previously attacked the US anywhere covered by Article 5 because of the geographic constraints of Article 6, and in retaliation for the acts of the US in that war that global terrorist network attacked, say, New York and D.C., then Article 5 would apply, there is no “well, you chose to fight them for other reasons before they attacked you” exclusion.

Now, if Russia only retaliated against French troops in Finland, Article 6 would geographically exclude Article 5 applicability.

I think there is a pretty large chance countries like Germany figure out some way to ignore that. IMO the only thing keeping a European country exempt from Russian military action is the presence of US forces.