Russia, Ukraine and the Ukrainian people.
Nobody else in the world has any influence.
All this talk of sanctions and diplomatic sanction will do nothing but drive the Ukraine closer to Russia.
Remember, very large majorities of the Ukrainian people in the east and south, the economic heart of the country...think these protestors are criminals. In fact about 1/2 the Capital City of Kiev thinks the same way. They are the ethnic Russians and their friends.
It's similar (though with great differences) to the US winning the Mexican war and then colonizing and $developing CA and TX at great cost over many generations.
Then the Mexicans rising up later to align with our "enemies".
Of course we did not undertake a genocide against the Mexicans being the greatest difference.
Still, Russia is HEAVILY invested in Ukraine, both blood and treasure. They lost at least 1/2 million soldiers defending it from the Nazis.
It's likely they're determined to keep it. It's also likely nobody can do a damn thing about it.
And several tens of thousands more killing Ukrainians.
Russian intervention is likely to produce an insurgency making Chechnya look like a cakewalk.