have turned ethnic Russians in eastern Ukraine into Ukrainian patriots. Putin might be able to capture part of what he wants but I sincerely doubt Russia can count on hanging onto it.
The problem is Crimea, a blob of land dangling down into the Black Sea. Oh, they might be able to hang onto that, it's been pretty peaceful since the takeover, but the only way they have to supply it is by ship. This whole war is about creating an over land corridor to Crimea, since their plan to take over all the Black Sea seaports didn't work.
This won't work long term, either. It would be an uninhabited, military corridor, horrendously expensive to maintain and under constant attack by both the Ukrainian military and armed civilians.
Putin's wakeup call was obviously the attack against the supply ships in a "safe" port. Unfortunately, the generals are preventing him from realizing that nothing on the Ukrainian mainland will be safe for an occupying force, ever.