For the purposes of this market, I will consider countries which are members of the OSCE. This is meant to be a proxy of "European country", but note that it also includes several (post-Soviet) countries which are geographically in Asia. I will not count the US and Canada.

! Any changes which result directly from the current Russia-Ukraine war do not count !

I will only count significant changes; I don't think there will be many opportunities for ambiguity, but, to give a formal criterion, the border change should affect at least 1.000 people. This is meant to rule out minor adjustments, e.g. to a border along a river which changes its course.

The obvious mechanisms for that would be secession (e.g. Scotland or Catalonia becoming independent) or conquest. If territory is exchanged, this will resolve if one country is universally considered to have lost territory on balance; an exchange largely considered to be fair/balanced does not count.

Both a de facto and a de jure change would count. For example, if Catalonia declares independence, either its recognition by the international community or Spain's loss of control over it would suffice for the market to resolve to Spain.

I will add new countries if needed (you can make suggestions in the comments), which will be split off from "other".