The Land of Oz is the main basis of L. Frank Baum's children book series, The Wizard of Oz. A vast realm filled with magical creatures, Oz is divided into four districts. On the Eastern front, it is the region of Munchkinland, while on the Western side there is the Winkie Country South front, with the South region being the Quadling Country, and the Northern region of Oz named the Gillikin Country, all surrounding the main capital of Oz, the Emerald City. It is ruled by its namesake and benevolent ruler, the Wizard of Oz, to preserve peace amongst citizens. Although, the realm is threatened by dark and nefarious forces including the Wicked Witches of the East and West, and the Nome King, it is saved by Oz's heroic subjects, as well as the transported girl Dorothy Gale.
Regarding the villain tournaments, Oz has been featured as one of the central locations of the live-action universe. While, in most of them, it is ruled by the villains, the second Disney Heroes vs. Villains War shows the realm as one of the main locations that's being guarded and defended by the the hero resistance.