The Mobian Badlands were a region of Mobius, specifically the continent of Northamer, located between the Overland and the Kingdom of Acorn's city of Mobotropolis, and was an area of hostility between the Overlanders and Mobians during the Great War. The Hedgehog brothers Jules and Sir Charles located the escaped convict Julian Kintobor in the Badlands in a routine scouting mission during the Great War, where he was rescued and brought back to the Kingdom. (StH: #50, SSS: #2)
During the subsequent reign of Julian/Dr. Ivo Robotnik, the Badlands were badly ravaged by the pollution incident to Robotnik's regime. During an expedition here, the Knothole Freedom Fighters were attacked by Robotnik using his new Beetle Bot vehicle, and nearly suffered a crushing defeat. Fortunately, they were saved thanks to magical powers obtained by Sonic the Hedgehog from special stones he had received for saving a mystical frog some time previously. It also served as the location for Princess Sally's Soul-Quest with NICOLE and the Knothole Freedom Fighters, and a path that Sonic took en route to the Robo-Hobo Jungle. (StH: #15, #40, IYF)
After Robotnik's death, Knuckles the Echidna somehow came across the Badlands while returning home from his adventures in Mercia and Albion. Locke and Sabre watched Knuckles confront a gang of bears on motorcycles, and were concerned by the now awakened use of Chaos powers, forcing a need for a meeting of the whole Brotherhood of Guardians. Knuckles used a Guiding Star Gem to return home from the Badlands. (KtE: #13, #14, #15)
In 3237, the Badlands was the battleground between a large SWATbot horde dispatched by the Eggman Empire, and the defences at Fort Acorn consisting of the Mes Braves Battalion, Chaotix, Amy Rose and a G.U.N. expedition force with Rouge the Bat. Ultimately, the SWATbot forces were destroyed by the combined defences, which ensured the force field around the irradiated Robotropolis was maintained. (StH: #131, #132, #133)