Not sure what you mean. My understanding is that this started with (corrupt) Yanukovych rejecting European Union agreement, wanting to maintain trading and lending ties with Russia.
Oh, my goodness. Not that you are entirely wrong: Yanukovych was Putin’s freaking handmaiden, corrupt on a level that makes Rod Blagojevich multiplied by Eliot Spitzer multiplied by (well, you get the picture) look like an amateur, and raping Ukraine’s constitution on a level that makes Obama look impotent. The EU agreement cancellation was a final straw, perhaps, but the Ukraine would have “blown” regardless of that or any Western meddling.
To really understand better, though, you have to at a minimum go back to WW2 (Ukraine was devastated horribly once by the Nazis and twice by Russia), and better yet, follow the relationship for at least the last several hundred years.
To understand the consequences of U.S. actions, “post Crimean invasion”, one must understand the basis of global security (such as it has been — no truly major wars) and relative lack of arms buildups from the end of the Cold War through 2008.