Aside from the Yugoslavia wars and (now) Russian adventures in Ukraine, there have not been significant efforts by central or Eastern European states to acquire territory at the expense of their neighbors since 1991.
I recall reading predictions at that time that a wave of irredentism was about to happen: Poland against Lithuania, Lithuania against Belarus, Hungary against Slovakia and Romania, Romania against Moldova, Turkey/Greece/Bulgaria, and so on-and I recall this being regarded as fairly likely, and not just a lunatic fringe position. But it didn't happen. Why not?
There are three big reasons for this: First, during the post Second World War period, there were huge population transfers. For the most part, you are talking about wide-spread deportations of people to their new 'homes' at worst, and stringent controls to eliminate minorities through assimilation at best. Most of the countries we are talking about are dominated now by particular ethnic groups. This is all information circa 1991/92.
So, we see there are some sizable minorities in some of these countries, but most of them are much smaller than they were pre-ww2. So, this limits the nationalistic fervor.
Second, we also have strong international organizations in place to help prevent this. The United Nations and NATO both operate as methods of control over any potentially ambitious state in the region. Let's look at a really easy example of this in the Yugoslav civil wars. Another way of characterizing these conflicts was Serb irredentism (albeit in quick reaction to secession by constituent parts of the Yugoslav state).
Finally, none of these states had the desire nor likely the capability to exert power outside their own borders (which helps explain the continued existence of places like Modolva and the independent regions of Georgia). I say desire, because most of these states, fresh off the toppling of communist dictatorships, were swept up in a democratic fervor that avowed cooperation. That said, while there was conflict (particularly in the Caucasian Republics) it was very limited in scale because none of these states had much in the way of capabilities. The fall of the Warsaw Pact and the USSR left governments in dis-array, militaries underfunded and under-equipped, and many soldiers out of a job. What conflict there was was mostly instigated and fought by militia type units rather than regular armed forces (the Nagorno-Karabakh War is an example of this; although the conflict itself also precipitated the rapid development and equipping of each respective side's army, the majority were basically militia type units).
Like you admit, it did, and in fact still is, going on. Besides the two examples you mention, there are widspread Hungarian claims over Slovakia, Transylvania and (to a lesser extent) Croatia and Serbia. Claims to a greater Hungary have had significant inpact on foreign relations in the region, leading to particulary tense relations with Slovakia at times. However, /u/Spoonfeedme is right to point out that the reason these irredentist claims are not nearly as prevalent as they had been in the interwar period is that the population transfers following the Second World War created fairly (but not entirely) homogenous nation-states. Hungary is probably the most significant exception in East-Central Europe, with large Hungarian minorities living in neighbouring countries: hence Hungary's notable irredentist claims.