How did the knowledge of great weapons like Bramhastra got lost in Hinduism tradition? As can be seen in Ramayan and Mahabharat, Gurus used to give knowledge of weapons to their shishya which were then used to protect Dharma. But eventually this knowledge was lost and Bharat couldn't fight invaders. How did this happen? Why weren't Devas invoked through yajnas when Sanatan Dharma followers were ethnically cleansed at the rate of millions by foreign invaders? At time of Mahabharat Indra himself helped Arjuna by granting him weapons. What happened now?