Is there a clear sharp line where e.g. Estonia is a "real" US interest and Crimea isn't? I mean NATO membership is a line, but it's not feeling as solid as it used to.
A next field of conflict is Belarus, which tries to distance itself from Russia. It's not NATO, it's not a country with a security guarantee like the Ukraine ( https://en.wikipedia.org/wiki/Budapest_Memorandum_on_Securit...) , it's not trying to connect itself to the EU (like the Ukraine), but still it could be a next conflict.
Then there are European countries not in NATO, but cooperating with NATO, like Sweden and Finland. Both have a border with Russia.
Sweden doesn't have a border with Russia. Also, as a Finn, I highly doubt Russia would attack Finland. We have a relatively good relationship with them, and such a war would be very costly with nothing to be gained. If there was a larger conflict in Europe, Russia might try to invade Åland or Gotland, but that also sounds unlikely to happen.
Belarus, really!?! They look like a fragment of the USSR that simply hasn't gotten the message yet. Where's the burgeoning democratic movement, where's the economic modernization?