The Serbian Autonomous Oblast of Krajina (Serbo-Croatian: Srpska autonomna oblast Krajina, Српска аутономна област Крајина) or SAO Krajina (САО Крајина) was a self-proclaimed Serbian autonomous region (oblast) within modern-day Croatia (then Yugoslavia). The territory consisted of majority-Serbian municipalities of the Republic of Croatia that declared autonomy in August 1990. It was formed as the SAO Kninska Krajina, but, upon inclusion of addition Serb-populated areas, changed its name simply to SAO Krajina. In 1991 the SAO Krajina declared itself the Republic of Serbian Krajina, and subsequently included the other two Serbian SAOs in Croatia, the SAO Western Slavonia and the SAO Eastern Slavonia, Baranja and Western Syrmia.
After the Croatian multi-party elections in 1990, ethnic tensions within Croatia increased. The Croatian President Franjo Tuđman was planning Croatia secession from Yugoslavia, so, in anticipation, Serb leaders created an autonomous region around the city of Knin. Initially, this was dubbed the SAO Kninska Krajina, but, after joining with the Association of Municipalities of Northern Dalmatia and Lika, it was renamed SAO Krajina in October 1990.
Kninska Krajina (English: Knin frontier) is a geographical and historical region in Croatia, part of the larger Zagora (hinterland) region. It is located around the town of Knin.
Kninska Krajina is situated between Bukovica in the southwest, Lika in the northwest, Drniška krajina (in Zagora) in the south, Cetinska krajina in the southwest, and (Završje) Bosnia and Herzegovina in the east.
In the 6th century, the region was settled by Slavs (Sklavenoi). Knin itself was first mentioned by Byzantine Emperor Constantine Porphyrogenitus (r. 913–959) as the centre of a parish under Croatian rule. At the request of King Peter Krešimir IV of Croatia (r. 1058–1075), Knin became an episcopal see. Demetrius Zvonimir of Croatia (r. 1075–1089) was seated in the town.
In the 15th century, the Ottoman Empire occupied the area resulting in most of the native population fleeing the region. It was largely abandoned and devastated as the Ottoman army advanced towards the north and west. The region was administrated into the Sanjak of Kirka.