Following an alliance contracted in 1912, Bulgaria, Greece and Serbia declared war on the Ottoman Empire. Their goal was to definitely expel the Ottomans from Europe. The First Balkan War started on 8 October 1912 and lasted six weeks. Serbians reached Skopje on 26 October. Ottoman forces had left the city the day before. During the conflict, Chetniks, a Serb irregular force razed the Albanian quarter of Skopje and killed numerous Albanian inhabitants from the city. The Serbian annexation led to the exodus of 725 Muslim families which left the city on 27 January 1913. The same year, the city population was evaluated at 37,000 by the Serbian authorities.