Putin took Crimea.
That's enough for me to put the blame squarely on Russia for the current situation. Whether the people who initiated the coup against Yanukovych represent the entire population, a majority or a minority, it's an internal Ukrainian affair and Russia has no business interfering.
Add the take down of the Dutch plane, the nonsense about tanks taking "relief supplies" over the border, soldiers getting "lost on vacation" and it's pretty clear that Putin is engaging in an illegal war.
And, yes, I am from the US. I don't agree with our illegal wars either so please don't go there.