High Quality Content by WIKIPEDIA articles! The decline of Buddhism in India, the land of its birth, occurred for a variety of reasons, and happened even as it continued to flourish beyond the frontiers of India.Buddhism was established in the area of ancient Magadha and Kosala by Gautama Buddha in the 6th century BCE, in what is now modern Uttar Pradesh and Bihar. Over the next 1500 years Buddhism became one of the region`s influential sects, spreading across the Indian sub-continent (see History of Buddhism).