According to Douglas Farah's article Harvard for Tyrants, Déby is an alumnus member of Muammar al-Gaddafi's training center.[2]
He moved to Sudan and formed the Patriotic Salvation Movement, an insurgent group, supported by Libya and Sudan, which started operations against Habré in October 1989.
He unleashed a decisive attack on 10 November 1990, and on 2 December Déby's troops marched unopposed into the capital, N'Djaména.