That's the trouble with self-determination. Which selves get to make the determination.
Kiev and Muscovy have a long history. There are many Muscovites who have lived in Ukraine for generations. The modern borders (post 1991) of Ukraine are based on the borders of the Ukrainian SSR which voted 90% for independence in August of that year.
Do we believe that the 10% should overrule the vast majority of the populace?
For years the new Ukrainian government looked east for support. But when a new government, that wanted to turn to the West took over, Russia moved in to "protect" its own interests. Sadly there were many turncoats in both the military and the government, and the sovereignty of the country was violated. The West looked away. As it had so many times in the past: Germany - 1953, Hungary - 1956, Czechoslovakia - 1968, Moldova -1992, Georgia - 2008.
So why should this time be any different?
For eight years, Russia's proxies, aided by Spetznaz and mercenaries had been fighting in Ukraine. Crimea had been annexed with the usual finger wagging and hand wringing in the West.
Some joker got himself elected president, whose biggest claim to fame was playing piano no-handed with his pants down. Nobody was going to DO anything. UN Security Coucil resolutions could be vetoed. And after a quick occupation, and some ineffective sanctions, things could settle down to normal. After all, the American president basically said that he might permit a "small incursion".
But, nooOOOoo! Turns out the reason the guy could play the piano with no hands is he's got balls of steel. Doesn't cut and run. Shames the collective "Great Western Powers" into backing him.
So, go ahead. Toss out those conspiracy theories about Nazis and George Soros and the Illuminati, and the Military Industrial Complex and the Gnomes of Zurich.