Query: Who intitiated Christianity to be a state church of the Roman Empire?
Context: The first known usage of the term in a legal context was in AD 380 by the Edict of Thessalonica of Theodosius I, which made Christianity the state church of the Roman Empire. Prior to the issuance of this edict, the Church had no state-sponsored support for any particular legal mechanism to counter what it perceived as "heresy".