Russia suffered more than any country in WW2. Russia never wants to see that happen again.
As long as Russias perceived enemies are weak, they aren't too much of a risk to Russia. Conversely, if Russias perceived enemies are getting stronger, it is a risk to Russia.
This book is a great eye-opener. It gives a very good explanation of why Russia has very good reason to be wary.
Also, Russia is a big country, with a spread of culture - some of which is quite un-European.
In the 1980s, I knew a couple of scientists who were working with in Russia on a couple of key projects. They frequently commented that Russian scientists had some very non-conformist views. One was that there was a massive layer of methane trapped beneath the earths crust that would power the earth for centuries. When I first read about shale gas, I wondered if they had been onto something.
Speaking for myself, I'd say that apart from the WW2 suffering, everything I wrote about Russia, could also apply to the US. They're quite happy to see their enemies kept weak - especially if it's cheaper than being strong yourself.
I imagine the Russians have worked out that every $ spent on Twitter is equivalent to $2 spent on arms.