It is much better if Putin is stopped now instead, but this crisis is not only about Ukraine, it is about all countries have the legal right to choose what organizations they want to belong to. If Ukraine wants to apply for a membership in the EU and NATO, they are free to apply for it. Furthermore, this has nothing or very little to do with NATO's expansion and how Russia perceive NATO. Russia's military power is more than enough to protect Russia from NATO, even if Ukraine became a member. It has more to do with having prosperous neighbors with a higher standard of living as neighbors. It can undermine his own political power if the Russians begin to demand the same.
The Ukrainians have closed off the water supply to the Crimean peninsula. I believe the attack will come from the Crimean and the main goal is to turn the water on and to connect the Donbass with the Crimean peninsula, but not before the Olympic Games in China.
1 There is no proof that Putin wants to go farther,thus there is no need to stop him ,
2 Ukraine (not ) having the right to choose what organisations it want to belong to ,is not our business,and also not a reason to fight for :we must only fight if our interests are threatened and a Russian attack on Ukraine is not threatening our interests .A Russian attack on Ukraine will only hurt Russian interests .
A Russian attack on Ukraine would before 1914 not raise eyebrows ,because statesmen before 12914 were realists .
We did not fight when Saddam attacked Iran,when the neighbours of Zaire invaded her,when China attacked Vietnam,etc,etc ,thus, why would we fight if Putin would invade Ukraine .
The only way to survive is to remember the following : if you want eternal peace,you will get eternal war .
And the Western policies since 1919 continue to prove this .
We have intervened everywhere on earth to impose our ideology and the result is a total failure .
Besides : NO European country will do something :sanctions are excluded as we are dependent on Russian gas and if the electors are denied food and warming they will held responsible the governments .
Last point :the standard of living in Ukraine is not higher than that in Russia ,but lower,much lower .