Slavonia (sləvōˈnēə) [key], Croatian Slavonija, historic region, part of Croatia. It is a fertile agricultural and forested lowland bounded, in part, by the Drava River in the north and the Sava River in the south. Wheat and corn are the major crops, and the leading industry is food processing. It also has rich oil and natural-gas resources. The population is largely Croatian and Serbian. Osijek is the chief city. The region was originally part of the Roman province of Pannonia. In the 7th cent. a Slavic state owing allegiance to the Avars was established. With Croatia, Slavonia was united with Hungary in 1102. It came under Turkish rule in the 16th cent. and was recovered by Hungary from the Turks through the Treaty of Karlowitz (1699). As a result of the Revolution of 1848, Hungary lost Slavonia, which was made an Austrian crownland, but in 1868 Slavonia was restored to the Hungarian crown and united with Croatia. It became part of Yugoslavia in 1918. When the Yugoslav constituent republic of Croatia declared its independence in 1991, Croatian Serb and Yugoslav forces seized control of portions of Slavonia and other areas in Croatia, but by late 1995 Serbs retained control of only E Slavonia, which was returned to Croatian rule in Jan., 1998.