After besieging the emperor at Salonica in 1340, he imposed a treaty assuring Serbia sovereignty over regions extending from the Danube to the Gulf of Corinth, from the Adriatic Sea to the Maritsa river, and including parts of southern Bulgaria up to the environs of Adrianople. Bulgaria had never fully recovered since its defeat by the Serbs at the Battle of Velbazhd. The outcome of the battle shaped the balance of power in the Balkans for the next decades to come and although Bulgaria did not lose territory, the Serbs could occupy much of Macedonia. Bulgarian tsar Ivan Alexander, whose sister Helena Dušan later married, became his ally between 1332 and 1365. Dušan ruled over major central part of the Balkan peninsula. He gave sanctuary to the former regent of the Byzantine Empire, John VI Kantakouzenos, in revolt against the government, and agreed to an alliance.