It was the attitude of the contemporary kings who were patronising Hinduism that led to the downfal of Buddhism. The attacks (invasions) of Vedic kings such as Chalukya Sudharma and of the foreign invasion by Hunas, Turks etc. also resulted in the decay of Buddhism. Besides all these, 'Vajrayan' ( the hardliner sect of Buddhism) also grew as a parasite on the host Buddhism.

The few important reasons that resulted in the downfall of Buddhism are:

1. A metamorphosis in the principles/ideology of Buddhism (i.e. emergence of Tantrayan, Mahayan)
   
   
2. Emergence of immoral and characterless Bhikshus.
   
   
3. Lack of patronage, previously accorded by emperors and kings.
   
   
4. The formation of the woman sangha and initiation of women as Bhikshunis.
   
   
5. The subsequent rise of Brahmanism and the attack of pro-Brahmin kings on Buddhism and its institutions.
   
   
6. Lacks of thinkers, philosophers and people who could perpetrate the religion.
   
   
7. The invasion of Hunas and Turks.
   
   
8. The cruel invasions of kings patronising Hinduism/Brahmanism like Pushyamitra, Shashank, Pulakesin II, Sudharma and subsequent invasions by Qutubuddin Aibak, Bakhtiyar Khilji (Turks) etc.
   
   
9. The Buddhists did not try to maintain a dialogue or a rapport with Hindus unlike the Jains.
   
   

Today, one can also see plenty of Buddhists in countries like Tibet, Bhutan, Nepal, Thailand and also the mountainous areas of India. One can see Buddhism alive, active and agile, having shades of Tantrayan and Mantrayan till date.