Stefan Dušan's sister, Jelena, had inherited from her husband, Mladen Šubić. In summer 1356, Louis invaded Venetian territories without a formal declaration of war. He laid siege to Treviso on 27 July. A local nobleman, Giuliano Baldachino, noticed that Louis sat alone while writing his letters on the banks of Sile River on each morning. Baldachino proposed the Venetians to assassinate him in exchange for 12,000 golden florins and Castelfranco Veneto, but they refused his offer because he did not share the details of his plans with them. Louis returned to Buda in the autumn, but his troops continued the siege. Pope Innocent VI urged the Venetians to make a peace with Hungary. The pope made Louis the "standard-bearer of the Church" and granted him a three-year tithe to fight against Francesco II Ordelaffi and other rebellious lords in the Papal States. Louis sent an army under Nicholas Lackfi's command to support the pope's troops in Italy. Louis marched to Dalmatia in July 1357. Split, Trogir, and Šibenik soon got rid of Venetian governors and yielded to Louis. After a short siege, Louis's army also captured Zadar with the assistance of its townspeople. Tvrtko I of Bosnia, who had succeeded Louis's father-in-law in 1353, surrendered western Hum to Louis, who claimed that territory as his wife's dowry. In the Treaty of Zadar, which was signed on 18 February 1358, the Republic of Venice renounced all Dalmatian towns and islands between the Gulf of Kvarner and Durazzo in favor of Louis. The Republic of Ragusa also accepted Louis's suzerainty. The Dalmatian towns remained self-governing communities, owing only a yearly tribute and naval service to Louis, who also abolished all commercial restrictions that had been introduced during the Venetians' rule. The merchants of Ragusa were explicitly entitled to freely trade in Serbia even during a war between Hungary and Serbia. Wars in the Balkans (1358–1370) Serbia started to disintegrate after the death of Stefan Dušan. According to Matteo Villani, an unidentified Serbian lord sought Hungarian assistance against his more powerful (and also unnamed) enemy in the late 1350s. Historians John V. A. Fine and Pál Engel write that the Serbian lord was a member of the Rastislalić family; Gyula Kristó and Iván Bertényi identify him as Lazar Hrebeljanović. Royal charters of 1358 show that Hungarian troops fought in Serbia in October 1358. The next summer Louis also marched to Serbia, but Stefan