Vladislav Vlaicu of Wallachia made an alliance with Ivan Shishman, a half-brother of the former ruler of Vidin, Ivan Sratsimir. Their united armies imposed a blockade on Vidin. Louis marched to the Lower Danube and ordered Nicholas Lackfi, Voivode of Transylvania, to invade Wallachia in the autumn of 1368. The voivode's army marched through the valley of the Ialomița River, but the Wallachians ambushed it and killed many Hungarian soldiers, including the voivode. However, Louis's campaign against Wallachia from the west was successful and Vladislav Vlaicu yield to him in next summer. Upon his initiative, Louis restored Ivan Stratsimir in Vidin. Ivan Stratsimir swore loyalty to Louis and sent his two daughters as hostages to Hungary.