- The US and its friends took a decade to intervene in Kosovo (one can start the clock anytime, but I choose to start the revocation of Kosovo's autonomy within Serbia) after years of both massacres and negotiations. Crimea happened immediately after Russia's stooge fled Kiev. Russia moved before any effort could be made to bargain, to send a peace keeping mission or preventative mission. this really is the key
- US and its friends did not conquer Kosovo and annex it. Russia did hold a sham referendum and annexed Crimea.
- Oh yeah, we could compare how the decisions were made. Kosovo's parliament voted for independence years after the local populace demanded it. Crimea's referendum happened shortly after Russia de facto occupied Crimea, the opponents were roughed up and/or arrested, and it is pretty clear that the results were just a bit fraudulent.
- Kosovo was after ... Bosnia, where the west had dithered while genocide happened. Oh, and Kosovo was also after Transnistria, where a Russian military unit essentially seceded from Moldova and after Russia's support for Armenian irredentism, and other Russian efforts in the former Soviet Union. Crimea was after ... Georgia where Russia did a nice job of playing Georgia and then created not one but two de facto independent states/failed states from territory carved out of Georgia.
- US and its friends did not use nuclear threats during the crisis or afterwards, although SACEUR Gen. Wesley Clark was determined to confront Russia's moves to Pristina. Russia has been making nuclear threats in many directions.
- The aftermath of American and Russian intervention tends to create failed states. In the former, this is mostly not intentional. In the latter, it is entirely intentional.
- After Kosovo, the US and its allies stopped. There was no more armed intervention in the Balkans but the US (ok, one minor effort to stop Macedonia from imploding in 2001). After Crimea, Russia launched a war in Ukraine, not just supporting separatists but sending its own forces, prolonging the conflict and violating ceasefires.
One can argue that all interventions are illegal, although responsibility to protect may suggest otherwise. Kosovo, whatever its flaws, was an effort to prevent further massacres after all other efforts had failed. Crimea and now Donbass are efforts by Russia to destabilize a neighbor after Russia lost its grip. Yes, we can compare the two, but the comparison reveals significant differences and only superficial similarities.