The solution to the Ukraine problem was diplomacy before it started, after it started, and now. Unfortunately for the West, diplomacy now will get them a worse deal than they could have had earlier. From Peter Van Buren at theamericanconservative.com:
The possible outcomes from the start of the war remain the same today.
From the moment Russian troops crossed into Ukraine, there were only two possible outcomes. Ukraine could reach a diplomatic solution that resets its physical eastern border (i.e., Russia annexes much of eastern Ukraine to the Dnieper River, and establishes a land bridge to Crimea), and so firmly reestablishes its geopolitical role as buffer state between NATO and Russia. Or, after battlefield losses and diplomacy, Russia could retreat to its original February starting point, and Ukraine would firmly reestablish its geopolitical role as a buffer state between NATO and Russia.
As of Day 286 on this fifth of December, despite much noise about nuclear war and regime change, those are still the only realistic outcomes. Diplomacy is necessary and diplomacy is sufficient to resolve the crisis in Ukraine. Until all parties realize that, and agree to sit down, the increasingly bloody and efficient meatgrinder will continue. The current status of the war—this 20th-century, WWI-style conquering of territory by creeping land advances with 21st-century weaponry—cannot continue indefinitely. Both sides will run out of young men to kill.
Vladimir Putin’s goal in his invasion has never been something quick and has never included Kiev. It has always been to widen the speed bump that is Ukraine between Russia and NATO. This problem for Putin is ever more acute as NATO builds up strength in Poland. While powerless to negotiate for itself at the fall of the Soviet Union, Russia was promised NATO would not expand eastward—a lie—and now Poland is sacrosanct NATO territory, as blessed as Paris, Berlin, and London, untouchable by foreign invasion.