Hi Neeta ji, Well, here's what happened Many of us do not know that Nepal wasn't a total Hindu Kingdom. Different people worshiped different gods. For instance, Newars practiced "Tantrism" (doesn't mean black magic) and Buddhism. Tantrism is still exist in Newar culture...take a look at the gods Newars worships...Bhairav, Kumari, and ect. During 4th to 9th century, Buddhism was major religion. Maha Pandit Shankaracharya was very worried about this situation, so he dedicated his life to revive Hinduism. After his visit to Nepal, Hindusim became dominant religion. Now how can Hinduism be practiced without Caste system? Hence, King Jayasthiti Malla introduced this system.