Stefan Uros III (Decanski), who rules Serbia from 1321 to 1331, has lost to the Bosnians the Adriatic lands conquered by his predecessor but has gained from the Bulgarians and Constantinople control over most of the Vardar River valley.

Stefan Dushan, as “young king”—too young to be able to pursue more active policies—governs the maritime provinces of the Serbian state.

He has to reconcile himself to the loss, in 1235, of the most westerly region of Serbia, …

… the land of Hum (later called Herzegovina) to Bosnian ban Stephen (Stjepan) Kotromanic, who, extending his domain southward, incorporates also the Adriatic coastline between Split and the Neretva River.

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.

Dušan, now that has conquered Epirus and Thessaly, seeks to obtain Constantinople.

To acquire the city, he needs a fleet.

Knowing that fleets of southern Serbian Dalmatian towns are not strong enough to overcome Constantinople, he opens negotiations with Venice, with which he maintains fairly good relations.

Venice fears a reduction of privileges in the Empire if Serbs become the masters of Constantinople over the weakened Greeks, but if the Venetians had allied with Serbia, Dushan would have examined existing privileges.

Once he became master of all imperial lands (especially Thessalonika and Constantinople) the Venetians would gain privileges.

Venice chooses to avoid a military alliance.

While Dušan seeks Venetian aid against the Empire, the Venetians seek Serbian support in the struggle against the Hungarians over Dalmatia.

When sensing that Serbian aid would result in a Venetian obligation to Serbia, Venice politely turns down Dušan’s offers of help.

Kantakouzenos tries to regain lands the Empire has lost while Dušan launches the Bosnian campaign (absent the Serbian troops in Macedonia and Thessaly).

In support, the Constantinopolitan patriarch Kallistos in 1350 excommunicates Dušan in order to discourage the Greek population in Dušan's Greek provinces from supporting the Serbian administration and thereby assist the Kantakouzenos campaign.

The excommunication does not stop Dušan's relations with Mount Athos, which still address him as Emperor, though rather as Emperor of Serbs than Emperor of Serbs and Greeks.

Kantakouzenos raises a small army and takes the Chalcidic peninsula, then Veria and Voden.

Veria is the richest town in the Botia region.

Dušan had earlier replaced many Greeks with Serbs, including a Serb garrison.

However, the remaining locals are able in 1350 to open the gates for Kantakouzenos.

Voden resists Kantakouzenos but is taken by assault.

Kantakouzenos now marches toward Thessaly but is stopped at Servia by Caesar Preljub and his army of five hundred men men.

The imperial force retires to Veria, and the aiding Turk contingent goes off plundering, reaching Skopje.

Dušan, once word of the imperial campaign reaches in Hum, quickly reassembles his forces from Bosnia and Hum and marches for Thessaly.

Bosnia’s hereditary ban Stjepan II Kotromanic, having reigned from 1314, has expanded his nation as far north as the Sava River and …

…annexed that part of Herzecgovina/Hum that lies west of the Serbian state ruled by Stefan Dusan.