To the people wondering why Russia wants Ukraine... it's not just about a "buffer". It's about sea ports. The West(USA+Europe) has been building bases, and batteries all around Russia, in an attempt to stifle its military potential.

Russia, looking forward, sees this trend continuing, until the point where its submarines(which carry their most formidable nuclear weapons abilities) can no longer freely roam, and fulfill MAD(Mutually Assured Destruction).

Russia fears that the circle around it of military bases, anti missle batteries will creep ever closer(as it has done in the last 3 decades), and it will eventually be forced to submit to western powers.

So, Rather than be squeezed by the west, like a boa constrictor year after year, Russia is taking action now. Ukraine offers many ports, as well as some resources. Russia's invasion of Ukraine isn't necessarily about the here and now, it's about reversing a 30 year old trend, that will result in Russia's eventual subservience to the west.

Russia didn't take this action unprovoked. It was a strategic move, used to counter the USA/Europe, who staged a political coup in Ukraine, to ensure it didn't fall into Russian hands. Russia blared this all over the internet, and used it to win the PR war with the west.

The reason the West can't really attack back, is because they started this, by illegally taking over the Ukraine with a puppet political party(who is heavily associated with bad things, like the Nazis... they even used Nazi symbols on their military uniform).