Circa 1497, Poland got attacked by Lituania and obviously lost it Swedish not interesting in getting into such mess. So I also attacked Poland and fed it the Marches, that put and end to the Polish threat. Polish fighting Lituania, that cannot be right!
In 1527, similar deal: Lituania went to war with Moscovy, its Bohemian ally itself being involved in war with Austria. I grabbed land and made it release Kiev. In the meantime I completely finished off Poland. Later, in 1643, Lituania was all alone in the world: same punishment, Polotsk was released and few provinces grabbed.
I went through the process of vassalizing Polotsk and Kiev (and momentarily Wallachia, to get the Full House achievement – a bit gamey, but less gamey than using England to release 6 subjects at starting date).
Lituania was later again allied to the Swedes. Which is historically odd. But, in 1660, they could not participate in war. Same punishment, I reduced Lituania so it could be, hopefully at the next war, diplo-annexed.
Having a tremendously big army, good finances, I decided, in 1665, to finish Bohemia, for the benefit of my marches – no real immediate gain, so. But surprisingly, Bohemia and german allies (Ansbach, Brunswick), managed to have constantly one stack of 50000 soldiers and two stacks of 25000. Even though I could indefinitely produce mercs, I was nonetheless gradually loosing territory. To the point I had to find the less horrible deal, instead of, like last time, getting weaker and weaker, risking that every other moron around would decide to attack me. Instead of feedings Marches, I actually weakened them. Once again, this was a case of was bad timing. And this bad timing came from gluttony.
And, yeah, at this speed, I wonder if it is even doable now to get core on all Russian areas, after wasting time in the west.