No, the situation is not one of kind. There are a few notable examples, and there would be likely many examples of locations that would really like for this to occur, but they do not have a regional superpower supporting them. The reason is that nationalism became a force in the early 20th century.
Nationalism is a belief, creed or political ideology that involves an individual identifying with, or becoming attached to, one's nation. Nationalism involves national identity, by contrast with the related construct of patriotism
There are different forms, but the important one here is called ethnic nationalism.
Some nationalists exclude certain groups. Some nationalists, defining the national community in ethnic, linguistic, cultural, historic, or religious terms...
The Nazis were nationalists that believed in radical ethnic purity. They annexed Austria and then the Sudetenland of Czechoslovakia with the support of these ethnic German communities and without military arms, since the Allies were trying to use appeasement with Germany and convinced the Czech government not to fight. Eventually warfare broke out in Czechoslovakia.
Yugoslavia was created through acts of diplomacy alone. It's proponents wanted a nation for Slavic people, so after WWI, the Allied Powers created the nation from several small Slavic kingdoms. Since the Ottomans and the Austrian Hungarian Empire were no longer able to fight, there was no further military conflict until WWII.