There are far bigger interests we hold in our hands than startling a war of these proportions. There surely are corruption and tensions going on, I do agree with your point, but you must look at the bigger picture in order to understand:
Look at the sanctions imposed by the European Union over Russia, which are still effective if I'm right; The EU did manage to make a huge fluctuation in Russia's economy, a very consistent one, but did this benefit EU anyhow?
Long story short, no. Russia was affected the most, but the EU did suffer, too, as the former boycotted some essential services and products to the latter, too. If you want to learn more about this situation, you can inform yourself on Google.
So, as you can see, Putin might be portrayed a lunatic in the perception of some people, but he's not dumb; he is NOT going to go any further with his imperialist attempts, because, well, he doesn't have any close allies: China wants to adopt as many western principles as possible ( it's already adopted capitalism ), Kazakhstan and its adjacent areas are too weak to carry any weight on themselves, and North Korea is only a joke.
Whereas the EU, USA, NATO members are strongly-tied one to another, which Putin is aware of. If he's not, well, he will endure the inevitable consequences of his oblivious actions. Quite straightforward.