Putin's end game... why is this in question? Putin simply wants to remain in power.
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Putin is a scum-bag dictator who cares most about remaining in power - at the same time, he's a nationalist, and would want nothing more for Russia to expand as much as possible, taking as many nations under its control as possible - as the leader of Russia this is a positive feedback scenario - I want to remain in power - the more nations under Russian sway the more power I have - the more nations I conquer/control, the more popular I become - the more popular I become, the better I'm able to remain in power - and so on...
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Russia is fucked up big time - the populace currently isn't anti-Putin enough to oust him IMO - so it's more of Putin until he dies. And once he dies some other despot will likely emerge.