A. What Was In Mind of the Mongols: The true faith of the Mongols in the most glorious Past was worshipping the Eternal Blue Sky and praying to Burkhan Haldun Mountain that had sheltered and saved Temujin and his family and to Chinggis Khaan himself.

Shamanism/Boo murgel/ or Tengerism:For thousands of years Central Asian nomads orrientated on Shamanism worshipping to the nature and Hokh Tenger\the Blue Sky\. Although it may look very primitive and simple at glance, the shamanism has indeed the most ancient backgrounds and a quiete sophisticated philosophy. Shamanism is a way of life in which a person believes that everything, a person, camel, a rock, a grass, an insect, water or water have a spirit which remains alive forever. A shaman's help is needed when a particular spirit is disturbed. Shaman can talk to nature, blue sky and spirits of somebody's ancestors. Chingis Khaan once created the Blue Tengerism or  "Blue Sky"  for the Mongols from the shamanism which became the main belief of Central Asian nomads and held a famous shaman under his favor.  The shamanism has still co-existed with Buddhism for the last four hundred years within certain geographic areas such as Buryatia in today's Siberia and north-eastern and northern Mongolia where Buryat, Darhad Mongols  and Tsaaatan or reindeer tribes live.

Buddhism: Unfortunately, the lamaism/"yellow religion"/, a kind of Buddhism was just  disastrious for thoughts of the Mongols.  Warrior spirit of the Mongols was washed away by this foreign religion causing to the downfall of the Mongols.

First indroduction: In 126O, when Hubilai, the grandson of Chinggis Khaan established Yan Dinasty in China, the Buddhism first time was introduced among Mongol rulers of China and it faded away after 100 years when the Mongols were expelled from China. The Mongols probably were afraid of being assimilated by Chinese./By the way, Semi-nomadic Tibetans who initially were of shaman believers too,  were converted to Buddhism by Indians. With the Indian Buddhism, the downfall of Tibetan Nation started/.

Second introduction: in 1570s, The Mongolian  khans/or "kings"/ and nobles started adopting so–called the “ Yelow Religion”, the sect of Tibetan Buddhism after Altan Khaan  of Tumed Mongols who was conducting military raids to Tibetan lands, was converted in to the buddhism. 
Nomadic lifestyle and physical similarities between the Mongols and the Tibetans and their mutual geographical distance from agricultural Chinese contributed to choice of this religion by Mongol Khaans. 

Third introduction: Then the turn of Manchus came who commenced rising since 1616. The Mongols purposely were introduced to Buddhism by the Manchus who in the begining had great difficulties on conquering them by military force. The Manchus succeeded to manipulate the Mongols. The Buddhism gradually spread among the Mongols throughout in 17th century. As result, abandoning  their spirit of resistance, most Mongols came to a spirit of  the retreat. In contrary to the North-American Indians,  who 500 years ago, immediately chose to resist Europian conquerors,  the Mongols-buddhists voluntarily moved away to deserts and arid mountains leaving their pasturing and farming lands to forChinese and Russian settlers.  A few  went resisting.  It would have been unthinkable on  the time of Chingis Khaan. For the last centuries, the Mongols never understood the sutras which were always read  in Tibetan language which is uncompehensable.  As result, we have today  Inner Mongolia and Buryatia, although the Buddhism succeeded to spread its roots more deeply among Halkha Mongols, the central Mongols. 

At time of the revolution of 1921, in Outer Mongolia had 650 monasteries and monks made up 40% of its male population. These factors provide some explanation as to how deeply the Mongols went down.

B. What is in Mind of Today's Mongols: 
Behavour of most Mongols in Mongolia now is blindly accepting everything from outsiders without critical gaze.