In the late 19th century, Kosovo was the centre of the Albanian National Awakening. Following their defeat in the Balkan Wars, the Ottomans ceded Kosovo to Serbia and Montenegro. Both countries joined Yugoslavia after World War I, and following a period of Yugoslav unitarianism in the Kingdom, the post-World War II Yugoslav constitution established the Autonomous Province of Kosovo and Metohija within the Yugoslav constituent republic of Serbia. Tensions between Kosovo's Albanian and Serb communities simmered through the 20th century and occasionally erupted into major violence, culminating in the Kosovo War of 1998 and 1999, which resulted in the withdrawal of the Yugoslav army, the establishment of the United Nations Interim Administration Mission in Kosovo and the declaration of independence in 2008. Serbia does not recognize Kosovo as a sovereign state and continues to claim it as its constituent Autonomous Province of Kosovo and Metohija, although it accepts governing authority of the Kosovo institutions as a part of the 2013 Brussels Agreement.