Ukraine is geographically much smaller than Russia, but Ukraine's population is 44 million vs. Russia's 146 million - not as big a difference as a map would make it seem. Further, Ukrainians are fighting for their national existence, are highly motivated, and have mobilized their entire manpower. Meanwhile, Russia has burned through many of its most elite military units and is reluctant to turn to conscription as it would be a sign that the war is going poorly. Ukraine receives a steady supply of increasingly advanced weaponry from the West, while international sanctions against Russia are hurting their resupply. After 6 months, Russia has been rolled back from Kiev, occupies only about 20% of Ukraine, and further progress has become glacial. A rational Russia would sue for peace and some territory and aim to undo sanctions. Of course, since Putin is a madman, we're unlikely to see that anytime soon. A grinding war lies ahead, but it's difficult to see how Putin achieves his maximal war aims.
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