The Hungarian-Austrian empire fell after WW1, leaving independent nations that we are familiar with today: Hungary, Austria, Czechoslovakia and Yugoslavia.
Its first impulse, is to want its stuff back. That is - the legal successor of the country, which was a dual country. What happens next is that Austria is taken out of the equation, with the rise of Nazi Germany, and the following absorption, but Hungary remains - and is now the only legal successor of the previous empire.
They would put reconstruction of the old imperial territory high on the agenda, and would seek to dominate all of Slovakia, Transsylvania, and if they could, as much of Yugoslavia as they could.
After WW2, and the crushing defeat of the Axis powers, Hungary has no longer had any official wish to control previous imperial territories. Afaik, Hungary has no official territorial claims on its neighbors, although in populations in Slovakia, Romania and Serbia there are many Hungarian communities who want a reunification with Hungary.
You also see Russia, having waited for a good moment, going through a long period of "Aw, let the past be past! A new Russia now! Going forward!" to them suddenly talking about Ukraine, Poland, the Baltic states, hell, official Ruskis have even brought up Finland as an interest of Russia, without being subtle either, the conquest of Finland is once again on Russian militaries minds. Not that this means much now, but the official line is that the past is the past, but ask people, and you'll often find out that grudges can last centuries.
During WW2 in particular, a lot of this "rebuild an old empire" was seen in Europe, Italy wanting to re-conquer mediterranean lands, hell even the Norwegian Quisling government sent formal requests to German leadership for an invasion of Sweden, so to recapture certain ex-Norwegian territories there (this was news to me up untill recently), they also had ambitions to retake Iceland and Greenland.
What I'm wondering is - does this have a name!? The act, of a nation, to officially seek to rebuild a previous manifestation of itself? Officially, in order to minimize tensions, most nations have no such ambition. But when shit hits the fan, these ambitions often come to the light.
