The origin of the Huns and their relationship to other peoples identified in ancient sources as Iranian Huns such as the Xionites, the Alchon Huns, the Kidarites, the Hephthalites, the Nezaks, and the Huna, has been the subject of long-term scholarly controversy. In 1757, Joseph de Guignes first proposed the Huns were identical to the Xiongnu. The thesis was then popularized by Edward Gibbon. Since that time scholars have debated the proposal on its linguistic, historical, and archaeological merits. In the mid-twentieth century, the connection was attacked by the Sinologist Otto J. Maenchen-Helfen and largely fell out of favor. Some recent scholarship has argued in favor of some form of link, and the theory returned to the mainstream, but the issue remains controversial.