Malebolgia

 was declared as the fifty-first state of the United States of America (AUDIO: Minuet in Hell) in 2003. (AUDIO: Neverland) It was located on the southeastern mainland, formed by the division of a pre-existing state. (AUDIO: Minuet in Hell)

In 2011, the Laughing Gnome astral projected William Bishop to Malebolgia in 2003. He ended up in the body of Gideon Crane, who "[lost] his marbles" shortly after. (PROSE: Rise of the Dominator)

Alistair Gordon Lethbridge-Stewart was sent there for an investigation, his cover suggesting he had helped establish the devolved parliament of Scotland and that he was there to offer the fledgeling state his experience and expertise.

The prime candidate for the first Governor was Brigham Elisha Dashwood III, an evangelist and politician who was also running the newly opened Brigham Elisha Dashwood Laboratory of Alternative Mentalities — a mental hospital. Behind the scenes, the hospital was a front for the newly re-formed Hellfire Club, which was working to ensure Dashwood's election with the help of the demon Marchosias.

The Eighth Doctor and Charley Pollard became involved with the Laboratory and the Club, and subsequently exposed Dashwood's activities, ending his political career. The Brigadier noted that "Malebolgia might actually become a quite decent new state" without Dashwood. (AUDIO: Minuet in Hell)

After Charley escaped from the Ever-and-Ever Prolixity, a Viyran agent was stationed in Malebolgia to search for her. (AUDIO: The Fall of the House of Pollard)

Legacy
Anne Travers of 2011 was familiar with Malebolgia being an American state. (PROSE: Rise of the Dominator)

Parallel universe
In 2040 of a parallel universe, the Doctor had credentials from Malebolgia State. (PROSE: Sustainable Energy)

Behind the scenes

 * The exact geographic location of this fictional state is never made clear. However, when Lethbridge-Stewart makes his first report he says gives his report's time in EST time zone. Combining that with the accents of some of its apparent residents suggests the location to be somewhere in the southeast.
 * The name Malebolgia comes from Malebolge, the eighth circle of Hell, as described in Dante's poem The Divine Comedy. In that book, the circle was reserved for the souls of liars, cheats, and frauds.

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