so, like what? sanctions? an appeal to the UN? a pr campaign?
I don't know.
But the West often manages to get its way without an invasion.
When Ukraine had a pro-Russia leader in 2013/2014 who wanted to more closely align the country with Russia rather than the EU, the West didn't have to start a war to stop that... they just sent funding and spooks to prop up a "mostly peaceful" protest movement (Euromaidan) that culminated in a coup d'état overthrowing the elected government and unconstitutionally installing a pro-EU, pro-NATO regime. Which then ruthlessly cracked down on counter-protesters from the other side (see
2014 Odessa massacre), and made sure to fuck over the ethnic-Russian/Russia-friendly provinces (banning their political parties etc.) before holding elections again.
All the while Western media was running a massive, spook-fed propaganda campaign romanticizing the coup as a heroic grassroots movement for "democracy" and "Western values", and pretentiously calling it the "Revolution of Dignity".
It's a dirty business, but you gotta give credit where credit is due - that worked out really well for the US and EU and their spooks, all the while they could pretend that they were not even "officially" involved.
A more savvy leader than Putin might have pulled the correct strings in the background to prevent Euromaidan from succeeding, and avoided the current situation entirely.
Or, instead of invading on a seemingly random day, hold off and simply promise to invade the day when Ukraine officially begins NATO membership talks - which would have put the ball in the other side's court, and may have worked as a deterrent.
Or just fund the break-away provinces (and supply them with weapons and Russian spooks) while pretending to not be officially involved.
Or diplomacy.
Very publicly offering a "peace summit" with the US president, is something that president may not have been able to ignore - be it Obama or Trump or Biden.
Or if you must go to war, maybe just seize the Russia-friendly provinces, in a way that makes it very clear that the scope is limited and you have no interest on marching on Kiev etc. - and may even get media images of the locals greeting your army as liberators.
Or any other less extreme solution. I don't know, I'm kinda retarded and not a foreign policy expert, but I just think that starting an full-scale invasion of an entire country is a fucking extreme measure, and - no matter what legitimate quarrels or concerns you may have had - makes you the aggressor and war criminal.