Dušan evidently wants to expand his rule over the provinces that had earlier been in the hands of Serbia, such as Hum, which had been annexed in 1326 by the Hungarian protégé and Bosnian Ban Stephen II Kotromanić.
Ban Stephen II had launched an attack in 1329, on Lord Vitomir, who held Travunia and Konavle.
The Bosnian army had been defeated at Pribojska Banja by Dušan, when he was still Young King.
The Ban soon took over Nevesinje and the rest of Bosnia.
Petar Toljenović, the Lord of "seaside Hum" and a distant relative of Dušan, sparked a rebellion against the new ruler, but he was soon captured and died in prison.
Dušan attacks Bosnia in 1350, seeking to regain the previously lost land of Hum and stop raids on his tributaries at Konavle.
Venice seeks a settlement between the two but fails.
He invades Hum in October with an army said to be of eighty thousand men, and successfully occupies part of the disputed territory.
Dušan according to Orbini had secretly been in contact with various Bosnian nobles, offering them bribes for support.
Many nobles, chiefly of Hum, are ready to betray the Ban, such as the Nikolić family, which is kin to the Nemanjić dynasty.
The Bosnian Ban avoids any major confrontation and does not meet Dušan in battle; he instead retires to the mountains and makes small hit-and-run actions.
Most of Bosnia's fortresses hold out, but some nobles submit to Dušan.
The Serbs ravage much of the countryside.
With one army they reach Duvno and Cetina; another reaches Krka, on which lies Knin (modern Croatia); and another takes Imotski and Novi, where they leave garrisons and enter Hum.
From this position of strength, Dušan tries to negotiate peace with the Ban, sealing it by the marriage of Dušan's son Uroš with Stephen's daughter Elizabeth, who would receive Hum as her dowry—restoring it to Serbia.
The Ban is not willing to consider this proposal.
Dušan may have also launched the campaign in order to aid his sister, Jelena, who n 1347 had married Mladen III Subic of Omis, Klis and Skradin.
Mladen had died in 1348 from Black Death (bubonic plague), and Jelena seeks to maintain the rule of the cities for herself and her son.
She is challenged by Hungary and Venice, so the Serbian army detachments in western Hum and Croatia may have been for her aid, as operations in this region were unlikely to help Dušan conquer Hum.
If Dušan intends to aid Jelena, rising trouble in the East precludes the plan.
