It clearly intends to connect at least enclaves in Moldova to the swath of southern Ukraine it seeks to take (having likely abandoned any near term prospect of displacing the Ukrainian regime generally), probably also at least parts of Georgia.
It may also seek to bring other CSTO members into the Russia/Belarus “Union State” and make that Union State into a tighter confederation. (And possibly not just by diplomacy; invasion of insufficiently cooperative clients is something that the USSR—hardly uniquely among major powers—did quite a lot of, and a Russian leader who openly sees the USSR as a prior incarnation of Russia whose empire was squandered and improperly dismantled might well turn to the same tactics to restore it.)
Beyond that, unless it can somehow neutralize NATO or is willing to go directly to war with it, Russia seems pretty constrained.
(Regarding how, I have no useful input. )
They _are_ nervous. Serbia might start acting Serbian again too
End This War - not Endless War
where did I see that?
Strategically speaking, Moldova and Baltic states, which Russia wants very much too, automatically become an easy prey in such a scenario. Russia really hates and very afraid of Intermarrium or anything resembling it. And Putin promised Lukashenko Baltic ports. Basically Russia is trying to make 4th partition of Poland and it starts to look like West Europe, though fortunately not US, start to give a bit of consideration to it.
Most probably Poland will get baited into the fight outside article 5 when Russia starts butchering deep inside Central and West Ukraine.
Poland loves the opportunity to bloody Russia, but they also love not being the ones to be bleeding for their sovereignty.
The rest of the world, at least the ones that stand to gain by weakening Russia, should absolutely follow in their footsteps.
Some idiots in the US have been crying that we've sent 1/3rd of our Stinger stocks to Ukraine, as if 1) the stinger is a desirable anti-aircraft platform and should be pushed as a mainstay of American defense, instead of an oldish system that could use a serious upgrade if we wanted it to be useful in a peer conflict, and 2) America actually relied on stingers at all, and didn't have the two largest air forces, designed specifically to murder peer adversary air forces.
Remember, as an American, your safety comes mostly from everyone being very far away. We could sent Ukraine our entire air force, and even though they wouldn't know how to use it, America would still have the largest air force in the world in our Navy! Anyone bitching about depleting our own defensive capability helping Ukraine is not arguing in good faith
There is usually not much of a choice. My ancestors from a nobility family (schlyahta) of Grand Douchy of Livonia from before the union with Poland were fighting Moscow Dukedom and later Russian Empire for half a millennia, with for example a far relative being among the leaders of the 1863 Polish uprising. (To their would be dismay i grew up in USSR and was for many years a "Great Russia" chauvinist, a disease very hard to treat :)
Also it's not like Europe sent so much there is nothing left. It's mostly stockpiles of older kit that was in reserve.
Plus Putin is not that insane to attack EU, his plan was revealed by an idiot that it is to go in Moldova next, then probably the other neighbors that are not in NATO yet.
It's a client, but not quite like (certainly, not as cooperative as) Belarus. But, for the USSR, that was true of Afghanistan before the Soviet invasion, too, but the invasion still happened.
And Kazakhstan turned down the public request Russia made for troops for Ukraine, a request that would not have been publicly made if Putin didn't expect a positive response, and declined to recognize the DPR and LPR.