You can refer to the following article by Molana Islahi for a brief history of Budhism and their current beliefs as well:
Essence of Polytheism (6)
The primary belief of Buddha was based on unitarianism thus making it a mystic religion at the core of it with ultimate slogan “I am God and I am the truth” thus making it a polytheistic notion as well. Wahdat-ul-Wajud among Muslim Sufi scholars is also another form of the same belief. The practices of current followers of Buddhism vary in different places. He is now worshipped as a god in China, Japan, Tibet, Burma etc and his magnificent statues and temples surprise many onlookers. His followers in China are also involved in worship of all kinds of ghosts, spirits, gods and goddesses (which is also form of polytheism). There is a worse situation in Tibet. The greatest religious priest of Tibet, the Dalai Lama, is believed to be Buddha’s incarnation and exercises godliness similarly. When the Dalai Lama dies there, every woman is desirous of giving birth to a new god and the new god is chosen through casting lots from among the children who are born during that period.