That is one massive Serbia.
No Serbian Krajina? Clearly wimps or traitors made this map. On a side note, I like to think the Ottomans reannexed Bulgaria and Greece in this.
It's extremely difficult to see, but top-right says "Serbia under emperor Dušan" - it includes territories that weren't really controlled legally (the part of Bulgaria, Bosnia and Srem, those were under military occupation, probably included because). Rest of Bulgaria (incl. all of Dobruja) were vassals. Another reason for these inaccuracies (well, not really, depends on what you count as ownership) - the smaller text says "according to a German map from Dušan's period, found in military archive in Pecs" and "Bulgaria is shown as a tributary state"
So not a war goal, but a historical map. Though we sought to restore those borders, until the governing elite fell for the yugo meme against the recommendations of, like, the entirety of the military who actually ventured into Croatia and saw the mentality there.
Though we probably will never find out just how much did Dušan manage to conquer and subjugate, our national library got bombed by the nazis deliberately, destroying pretty much probably the only copies of some ancient shit, bits and pieces of which are found in the most random locations (primarily Russia)