Doing this through purely diplomatic means, without waging any war, except for a phony war with Jacobin rebels, was the greatest diplomatic achievement of 19th century History, as was convincing the Bear to not curbstomp them before they could conclude such. Funnily Finland is the only country that can achieve this without wars in APD.
Then they kept electing candidates from the only party that only allows Finns to vote(Residency)
And Finland-dominated Scandinavia took a big slice of Central Africa later, consolidating their status as a newly established Great Power.
Anyway, I think this is now in page 3, so update is coming
PS: There is also a "Form Greater Finland" decision, but for some reason it is unavailable to Democracies.