With the same impetuosity that had carried them to the foothills of the Rhodope Mountains after the capture of Adrianople, the Osmanlis crossed the Vardar in 1372, and pushed their arms into Old Serbia, Albania, Bosnia, and even to the mountains of Dalmatia, from which they could see the Adriatic.[340] Other adventurous bands, eager to attract the attention, the commendation, and the rewards of Murad, followed the footsteps of the Catalans, traversed Thessaly, and appeared in the plains of Attica.[341] Murad destroyed the Macedonian empire of Stephen Dushan without great effort. The Serbians remaining east of the Vardar, nobles and peasants, became Ottoman subjects. In upper Serbia, they rallied round one of their number, Lazar Gresljanovitch, whom they formally elected as successor of the Serbian kings. But Lazar was so weak that he did not take the title of emperor (_tzar_) or of king (_kral_), but called himself merely prince (_knez_).[342] To secure the existence of his kingdom or principality, he sought peace with Murad, and, following the example of the Byzantine and Bulgarian rulers, became vassal and tributary of the Ottoman emir.[343] X Before the end of the year 1372, it was recognized that the Osmanlis had come into the Balkans to stay. The conquest of Macedonia east of the Vardar, following so closely upon the subjugation of southern Bulgaria and the completion of the Thracian conquest, gave to Murad a preponderant position in the Balkan peninsula. The Byzantine emperor and the Bulgarian and Serbian princes were his tributaries. Wallachia, Bosnia, Albania, Epirus, Thessaly, Attica and the Peloponnesus were now on the confines of the Ottoman Empire, and menaced by Ottoman invasion. In Europe, Murad was credited with having the intention of invading Hungary. It was reported that he had made an alliance with the Tartars of Russia to attack Hungary. The Tartars were to cross the Carpathians by way of Moldavia into Transylvania, while Murad was to work his way up the valley of the Danube.[344] Murad may have dreamed of such a project, just as he had thought of making a supreme effort to enter Constantinople after his first Thracian campaign. But, if he did, he was deterred by the same well-grounded fear of moving too fast. Ten years before he had refrained from committing a fatal error. He would continue to make haste slowly. The early Osmanlis were not raiders. They were empire-builders. They succeeded because they never forgot that their greatest problem was that of assimilation. When they extended their conquests beyond the area of possible assimilation, the period of decay automatically commenced.