Quotation:
"Buddhism has the characteristics of what would be expected in a cosmic religion for the future: it transcends a personal God, avoids dogmas and theology; it covers both the natural & spiritual, and it is based on a religious sense aspiring from the experience of all things, natural and spiritual, as a meaningful unity" Albert Einstein



Overview:
Buddhism is the fourth largest religion in the world, being exceeded in numbers only by Christianity, Islam and Hinduism. It was founded in Northern India by the Buddha, Siddhartha Gautama. He was born circa 563 BCE in Lumbini which is in modern-day Nepal. At the age of 29, he left his wife, children and political involvements in order to seek truth. It was an accepted practice at the time for some men to leave their family and lead the life of an ascetic. He studied Brahmanism, but ultimately rejected it. In 535 BCE, he attained enlightenment and assumed the title Buddha (one who has awakened).

He is also referred to as the Sakyamuni, (sage of the Sakya clan). He promoted The Middle Way, rejecting both extremes of the mortification of the flesh and of hedonism as paths toward the state of Nirvana. He had many disciples and accumulated a large public following by the time of his death in his early 80's in 483 BCE.

Two and a half centuries later, a council of Buddhist monks collected his teachings and the oral traditions of the faith into written form, called the Tripitaka. This included a very large collection of commentaries and traditions; most are called Sutras (discourses).

As Buddhism expanded across Asia, it evolved into two main forms, which evolved largely independently from each other:

Theravada Buddhism (sometimes called Southern Buddhism; occasionally spelled Therevada) "has been the dominant school of Buddhism in most of Southeast Asia since the thirteenth century, with the establishment of the monarchies in Thailand, Burma, Cambodia and Laos."
Mahayana Buddhism (sometimes called Northern Buddhism) is largely found in China, Japan, Korea, Tibet and Mongolia.

To which might be added:

Tibetan Buddhism, which developed in isolation from Theravada and Mahayana Buddhism because of the isolation of Tibet.

Since the late 19th century:

Modern Buddhism has emerged as a truly international movement. It started as an attempt to produce a single form of Buddhism, without local accretions, that all Buddhists could embrace.