They neutralised Georgia after Georgia attacked and killed several of their soldiers.
They seized (bloodlessly I might add) Crimea after the new western-imposed government threatened to end the perpetual lease of the Sevastopol naval base. I might also add that 'Maidan' was the 2nd western-sponsored 'revolution' in Ukraine in a decade.
Now Russia is defending a long-time ally in the middle east from western-backed terrorists.
Then there's also NATO advancing all around Russia, the various 'defensive' missile systems being installed by US-allied countries who happen to encircle Russia, etc...
> Could you count how many times in history yielding to bold advances of power hungry ruler served as effective deterrent to war?
The only one making bold advances is the US, and yes, Russia isn't yielding, and the US is making it a problem. But you're right, it is a deterrent to war - if a weak ruler like Yeltsin were still in power Russia would probably be in another dozen pieces right now, with wars raging in half of them...