Serbia is a country situated in the central Balkans and borders Hungary to the north, Romania to the northeast, Bulgaria to the southeast, North Macedonia to the south, Croatia and Bosnia and Herzegovina to the west, and Montenegro and Kosovo to the southwest. The territory of modern-day Serbia faced Slavic migrations in the 6th century, establishing several regional states in the early Middle Ages at times recognised as tributaries to the Byzantine, Frankish and Hungarian kingdoms. The Serbian Kingdom obtained recognition by the Holy See and Constantinople in 1217, reaching its territorial apex in 1346 as the relatively short-lived Serbian Empire. By the mid-16th century, the Ottomans annexed the entirety of modern-day Serbia; their rule was at times interrupted by the Habsburg Empire, which began expanding towards Central Serbia from the end of the 17th century while maintaining a foothold in Vojvodina. Following casualties in World War I, and the subsequent unification of the former Habsburg crownland of Vojvodina (and other lands) with Serbia, the country co-founded Yugoslavia with other South Slavic nations, which would exist in various political formations until the Yugoslav Wars of the 1990s.