Putin cites Kosovo as legal grounds to partition Ukraine.
Kosovo was/is in the heartland of historical Serbian territory. During its time under Ottoman occupation, it went through a period of colonization comparable to the "Rusification" of former USSR states (i.e., ethnic resettlement and deportation). There was a violent and orchestrated demographic shift to favour the occupiers.
The "West" (i.e., most of NATO and the EU) decided that the current demographics of the region warranted partitioning Serbia despite the fact the fact that Kosovo was legally Serbia.
I realize that there were a lot of security/humanitarian issues at the time that are not present in Crimea and the situation was a lot more volatile, but if you keep it as simple as foreign military intervention and partitioning of a nation state, I think there are a lot of similarities. At the time, Russia in fact warned that they would consider it a precedent (although they are just as hypocritical here because they do not recognize Kosovo).
Edit: Sorry, this is why I thought that it was relevant:
http://cnsnews.com/news/article/patr...sovo-precedent
Putin is trying to use it as justification.