Other cities in Slavonia have populations below 20,000. According to the 2001 census, Croats account for 85.6 percent of population of Slavonia, and the most significant ethnic minorities are Serbs and Hungarians, comprising 8.8 percent and 1.4 percent of the population respectively. The largest portion of the Serb minority was recorded in Vukovar-Syrmia county (15 percent), while the largest Hungarian minority, in both relative and absolute terms, was observed in Osijek-Baranja county. The census recorded 85.4% of the population declaring themselves as Catholic, with further 4.4% belonging to Serbian Orthodox Church and 0.7% Muslims. 3.1% declared themselves as non-religious, agnostics or declined to declare their religion. The most widely used language in the region is Croatian, declared as the first language by 93.6% of the total population, followed by Serbian (2.6%) and Hungarian (1.0%). The demographic history of Slavonia is characterised by significant migrations, as is that of Croatia as a whole, starting with the arrival of the Croats, between the 6th and 9th centuries. Following the establishment of the personal union of Croatia and Hungary in 1102, and the joining of the Habsburg Monarchy in 1527, the Hungarian and German speaking population of Croatia began gradually increasing in number. The processes of Magyarization and Germanization varied in intensity but persisted until the beginning of the 20th century. The Ottoman conquests initiated a westward migration of parts of the Croatian population; the Burgenland Croats are direct descendants of some of those settlers. To replace the fleeing Croats the Habsburgs called on the Orthodox populations of Bosnia and Serbia to provide military service in the Croatian Military Frontier. Serb migration into this region peaked during the Great Serb Migrations of 1690 and 1737–39. Following the collapse of Austria-Hungary in 1918, the Hungarian population declined, due to emigration and ethnic bias. The changes were especially significant in the areas north of the Drava river, and Baranja County where they represented the majority before World War I. Since the end of the 19th century there was substantial economic emigration abroad from Croatia in general. After World War I, the Yugoslav regime confiscated up to 50 percent of properties and encouraged settlement of the land by Serb volunteers and war veterans in Slavonia, only to have them evicted and replaced by up to 70,000 new settlers by the regime during World War II.