A historical region of Croatia between the Drava and Sava Rivers. Originally part of the Roman province of Pannonia, it became a Slavic state in the seventh century and has long been allied with Croatia. Part of Yugoslavia after 1918, Slavonia was invaded by Serbia in 1991 following Croatia's declaration of independence from Yugoslavia. Croatia regained control of western Slavonia in 1995 and eastern Slavonia in 1998.