Russians could invade and while it is most likely that after a long war they'd be pushed back, they'd still leave ruins.

Also, we don't have unified army. So as painful as it is, it is most likely Baltic states would have to fend of with their military (and due to population, well, they can't - even if they are bringing conscription back), maybe Poland and Finland. Maybe. And then you'd have to coordinate what to do next between all national militaries.

And what would stop a Frenchman or Portuguese to say Why die for Vilnius?

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