From the start, if we think in realpolitical terms, we let him effectively keep Crimea and Donbas/Luhansk without giving the Ukraine material support to take them back, out of the fear of pouring fuel into the fire.
Putin had demands that were de facto impossible to fulfill, they read as if the US/European governments had power over e.g. the desires of the inhabitants of the Baltic states. They all wanted into the EU/NATO after the Cold War for reasons that aren't hard to empathize with.
In a security-political sense, making concessions that impact your weakest allies is a surefire way to destabilize your own alliance.
Also, why do we have to make concessions in terms of Ukraine and guaranteeing that Ukraine won't join EU/NATO? Putin should have been talking to Ukraine about that and giving concessions to Ukraine in exchange for staving off any alliance memberships - but it's now clear why he didn't.
Putin had demands that were de facto impossible to fulfill, they read as if the US/European governments had power over e.g. the desires of the inhabitants of the Baltic states. They all wanted into the EU/NATO after the Cold War for reasons that aren't hard to empathize with.
In a security-political sense, making concessions that impact your weakest allies is a surefire way to destabilize your own alliance.
Also, why do we have to make concessions in terms of Ukraine and guaranteeing that Ukraine won't join EU/NATO? Putin should have been talking to Ukraine about that and giving concessions to Ukraine in exchange for staving off any alliance memberships - but it's now clear why he didn't.