Now it's America that's meddling in Russia's back yard, so Putin took action.
The Soviet missiles that were put in Cuba were a direct threat to the United States. What threat is there against Russia in Ukraine?
You need to think like a Russian. If you were Russian, you would have studied Napoleon's invasion, and you would have older relatives who personally experienced Hitler's invasion.
For self-defense, you would want the Ukraine in Russia's orbit. Just as the USA wants Canada in the USA's orbit.
I'm not saying that Putin is correct, or that the Russian mind-set is correct. I'm not defending either one. But to understand Russian politics, you need to think like a Russian.