Buddhism has deep roots in Mongolian culture and history. Historians believe the first "contact" between Buddhism and Mongolia was made in the first millennium AD. Since then Buddhism has been cast out and introduced back multiple times. During the Mongolian Empire era, it was the de facto state religion of Mongolia. Even going as far as developing a new language integrating both Tibetan script and Mongolian script. After the Mongol Empire fell the Mongolians returned to the shamanic traditions. Since then until 20th-century, Mongolian Khans trying to get the support of Tibetan Buddhism established head of many schools.
During early 20th-century Ikh Huree, as Ulaanbaatar was then known, was the seat of the preeminent living Buddha of Mongolia (the Jebtsundamba Khutuktu, also known as the Bogdo Gegen and later as the Bogd Khan), who ranked third in the ecclesiastical hierarchy after the Dalai Lama and the Panchen Lama. In the 1920s, there were about 110,000 monks, including children, who made up about one-third of the male population, although many of these lived outside the monasteries and did not observe their vows. About 250,000 people, more than a third of the total population, either lived in territories administered by monasteries and living Buddhas or were hereditary dependents of the monasteries. It is believed during this time the Monasteries controlled an estimated 20 percent of the country's wealth. Some nobles donated a portion of their dependent families—people, rather than land, were the foundation of wealth and power in old Mongolia—to the monasteries. Some herders dedicated themselves and their families to serve the monasteries, either from piety or from the desire to escape the arbitrary exactions of the nobility.
When the revolutionaries took power, determined to modernize their country and to reform its society, they confronted a massive ecclesiastical structure that enrolled a larger part of the population, monopolized education and medical services, administered justice in a part of the country, and controlled a great deal of the national wealth. After the revolution the Soviet Union's influence in Mongolia was strong. To strengthen their control over Mongolia, Stalin and NKVD organized a purge. During 1937-1939, the dark spot in Mongolia history known as "The Great Repression" happened. During this period many high ranking politicians and lamas /monks/ were arrested, tortured, and killed under false acquisitions. By the end of this Great Repression, 746 of the country's monasteries were liquidated and burned and 18,000 counterrevolutionary lamas were executed. Monks that were not executed were conscripted into the Mongolian armed forces or otherwise forcibly laicized.
After the fall of the Soviet Union, mass graves of monks executed during the repressions were uncovered in 1991 and 2003. There are a museum and a monument dedicated to victims of the repression in Ulaanbaatar. At the same time, there have been concerted efforts by various groups to restore many of the temples and monasteries that were destroyed during the purges.
I. Gandantegchinlen Monastery
The Gandantegchinlen Monastery is a Mongolian Buddhist monastery in the Mongolian capital of Ulaanbaatar that has been restored and revitalized since 1990. The Tibetan name translates to the "Great Place of Complete Joy". It currently has over 150 monks in residence. It features a 26.5-meter-high statue of Avalokiteśvara. It came under state protection in 1994.
Gandantegchinlen Khiid monastery, having escaped mass destruction, was closed in 1938, but then reopened in 1944 and was allowed to continue as the only functioning Buddhist monastery, under a skeleton staff, as a token homage to traditional Mongolian culture and religion. With the end of the Soviet Union in Mongolia in 1990, restrictions on worship were lifted.
II. Erdene Zuu Monastery
The Erdene Zuu Monastery is probably the earliest surviving Buddhist monastery in Mongolia. Abtai Sain Khan, the ruler of the Khalkha Mongols and grandfather of Zanabazar, the first Jebtsundamba Khutuktu, ordered the construction of the Erdene Zuu monastery in 1585 after his meeting with the 3rd Dalai Lama and the declaration of Tibetan Buddhism as the state religion of Mongolia.
Three small temples and the external wall with the stupas survived the initial onslaught and by 1944 Joseph Stalin pressured Choibalsan to maintain the monastery (along with Gandantegchinlen Monastery in Ulaanbaatar) as a showpiece for international visitors, such as U.S. Vice President Henry Wallace, to prove that the communist regime allowed freedom of religion.
III. Amarbayasgalant Monastery
Amarbayasgalant Monastery or the "Monastery of Tranquil Felicity", is one of the three largest Buddhist monastic centers in Mongolia. The monastery was established and funded by order of Manchu Yongzheng Emperor(and completed under his successor the Qianlong Emperor) to serve as a final resting place for Zanabazar (1635–1723), the first Jebtsundamba Khutuktu, or spiritual head of Tibetan Buddhism for the Khalkha in Mongolia and a spiritual mentor to both emperors' ancestor, the Kangxi Emperor.
Amarbayasgalant was one of the very few monasteries to have partly escaped destruction during the Stalinist purges of 1937, after which only the buildings of the central section remained. Many of the monks were executed by the country's Communist regime and the monastery's artifacts, including thangkas, statues, and manuscripts were looted, although some were hidden until more fortunate times.