First Rajgir, Second vaishali, Third patliputraFourth Buddhist Council is the name of two separate Buddhist council meetings first in Sri Lanka and another at Sarvastivada school, in Kashmir around the First Century AD.
Universal soul is one of the main Keystone of the philosophy and the thought of the Upanishad. Brahma satyam Jagat Mitya Jeevo Bramanah Parah talks about the impermenance of the body and its existence.
Greeks, Kushanas & Shakas had entered India through the North West side. Accepting the local religion would provide them the easiest way to achieve legitimacy of their rule. Since Buddhism was prevalent in the area at that time and it was provided easiest entry (Hinduism had st5rict caste based structure) so, they embraces Buddhism.