Stefan Dušan
War with the Bosnian banate

Dušan evidently wanted to expand his rule over the provinces that had earlier been in the hands of Serbia, such as Hum, which was annexed by Bosnian Ban Stephen II Kotromanić in 1326. In 1329, Ban Stephen II launched an attack on Lord Vitomir, who held Travunia and Konavle. The Bosnian army was 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.

In 1350, Dušan attacked Bosnia, seeking to regain the previously lost land of Hum and stop raids on his tributaries at Konavle. Venice sought a settlement between the two but failed. In October he invaded Hum, with an army said to be of 80,000 men, and successfully occupied part of the disputed territory. According to Orbini, Dušan had secretly been in contact with various Bosnian nobles, offering them bribes for support. Many nobles, chiefly of Hum, were ready to betray the Ban, such as the Nikolić family, which was kin to the Nemanjić dynasty. The Bosnian Ban avoided any major confrontation and did not meet Dušan in battle; he instead retired to the mountains and made small hit-and-run actions. Most of Bosnia's fortresses held out, but some nobles submitted to Dušan. The Serbs ravaged much of the countryside. With one army they reached Duvno and Cetina; another reached Krka, on which lay Knin (modern Croatia); and another took Imotski and Novi, where they left garrisons and entered Hum. From this position of strength, Dušan tried 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 was not willing to consider this proposal.

Dušan may have also launched the campaign to aid his sister, Jelena, who married Mladen III Šubić of Klis, Omiš and Skradin, in 1347. Mladen died from Black Death (bubonic plague) in 1348, and Jelena sought to maintain the rule of the cities for herself and her son. She was challenged by Hungary and Venice, so the dispatch of Serbian troops to western Hum and Croatia may have been for her aid, as operations in this region were unlikely to help Dušan conquer Hum. If Dušan had intended to aid Jelena, rising trouble in the East precluded this. Pope Clement VI in 1335 addresses to King Stefan Dušan and request him to stop the persecution and that to the bishop of Kotor which is responsible for Roman Catholic Diocese of Trebinje return monasteries, churches, islands and villages, which some kings of Raška before him overtook.
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