The Upanishads, which are actually a part of the Vedic literature, lay emphasis on simple life and true actions.
    There are about 300 Upanishads but the most famous among them are Isa, Katha, Taittiriya, Aitareya, Chandogya, Brahadaranyaka etc.

*    Causes of the Rise of jainism and buddhism
    The simple varna system had degenerated into a rigid caste system. The high-caste Hindus developed hatred for the low-caste people, most of whom were branded as Shudras or untouchables who were subjected to abject humiliation, suffering and misery.
    It was during this  period of religious degeneration and social persecution of the common people that two great teachers, Mahavira Vardhamana and Gautama the Buddha, preached to them the path of love, kindness and piety. They denounced the rigidity of      the caste system and condemned the practice of untouchability.