Aymguud is word from the Mongolian and Trukic languages with the original meaning of the “tribe”. In Mongolia it is the name of the top-level administrative divisions. Each Aymag is subdivided into several somon. The capital Ulaanbaatar is adminsistrated separately as a federal district. The Aymguud of Mongolia are divided into 312 Somon (“districts”).
Towards the ed of the Qing Dynasty of the Manchu in China. the territory of Quter Mongolia was divided into the khanates Khowd, Jassaktu, Sain-Noin, Tushetu, and Tsetse. After the Mongolian declaration of independence of 1921, the provinces of Ala Sahn, Ordos, Silin Gol, and Chearim remained with China, and Tannu Tuva became the independent Urjanchai Republic (today the autonomous Tuva Republic in Russia). The new People’s Republic of Mongolia left the existing administrative subdivisions in place at first.
After the end of the Soviet-Japanese Border Wars (1938-19390) an administrative reorganisation was initiated in 1921, which resulted in the Aymags Arhangay, Choibalsa, Dornogovi, Zavhan, Hentiy, Hovd, Huvsgul, Umnugovi, Ovorhangay, Tuv, and Uvs. A long strip of the souther Govi fell back to China in 1954. The subdivision of the remaining Mongolia was then refined, creating the Aymags Bayanhongor, Bayan-Ulgiy, Bulgan, Dundgovi, Govi-Altay, and Suhbaatar. The Selenge Aymag was split from Tuv Aymag two years later.
The Choibalsan Aymag was renamed to Dornod Aymag in 1963 and the capital Ulaanbaatar was split from Tuv Aymag as a federal district. The same status was given to the newly founded industrial cities of Darhan (1961 in the Selenge Aymag) and Erdenet (1975 in the Bulgan Aymag). In 1994, two Somon of the Bulgan Aymag were taken to built the Orhon Aymag around Erdenet, and four Somon of the Selenge Aymag to built the Darhan-Uul Aymag around Darhan, ending the special status of the two cities. The Gobisumber Aymag was split from the Dornogove Aymag in 1996.