By 1360 the various Balkan states were becoming increasingly fragmented as internal rivalries and the rise of the Ottoman Empire began to take effect. With a victory near Gallipoli, the Ottomans acquired their first territory in Europe in 1354, whilst Wallachia returned to the Kingdom of Hungary as a vassal in the same year. After the death of the king of Serbia, Stefan Dušan, in 1355, the Serbian Empire began to disintegrate. His son and heir, Stefan Uroš V, proved incapable of keeping the powerful nobility in check so they began to claim territory for themselves. At the same time, his uncle Simeon Uroš laid a rival claim to the throne, which resulted in both men controlling their own small empires within Serbia, with different nobles pledging allegiance to each. Hungary capitalized on the internal divisions within Serbia by launching attacks on the border territories, which were loyal to Stefan Uroš V.