Johann, I am uncertain s to your point of reference. The Sikhs are thought to be a combination of Hinduism and Islam. Zen Buddhism is thought to be a combination of Buddhism, Confucianism and Taoism.
Buddhism: It arose in the mid-sixth century BCE, at the same time as Zoroasterism, Jainism, Confucianism and Taoism. Also, this was the time of Jeremiah, Ezekiel and Daniel of the Old Testament. NOTE: I once knew an Adventist who took the position that the world was ripe, at this time, for a fulfillment of the ancient Old Testament prophecies relating to the nations comming to Isreal to be taugnt spiritual truth and that it wsa the failure of Isreal to fill lthis role that led to the development of these other religions. An interesting thought.
Hinduism: It developed out of the Sanskrit speaking Aryan tribes that invaded India n the 2nd Millennium BCE. It is associated with the polytheistic religions closely related to Greece, Rome and Iran. In its developent it formulated one creator god, called Brahman, who manifests himself in 360 million forms. As such, it becam a kathenotheistic religion, rather than a monotheistic one. A critical belief is that action is more important than belief. As such, a person who properly verbalizes the name of the god Krishna, incarnates that god on earth regardless of personal belief. Hinduism exists in many sects, one of which, Yoga, is often not considered to be the religion that it actually is.
It is of interest that devout Hindus might deny that Hinduism is a religion. It does not meet the classicial defination of a religion. It does not have an individual founder. It has a vague relationshilp to authoritive scripture (The Reg Veda which dates to about 1,000 BCE.) and it lacks a single set of isseus that define it.
As to its history: It is believed to have some background prior to the Aryan invasions of India. But, this period has little historical documentation.
The historical background that we have traces Hinduism to the Vedic Period which is dated from 5,000 BCE to about 1,500 BCE.
Following the Vedic Period, about 1,000 BCE, Hinduism changed from a positive view of life to a pessimistic one in which the focus was on escape from the world, Karma developed and transmigration of the soul became a belief, with absorption into the world-soul of Brahaman became the spiritual goal. Yoga, in its several sects developed at this time.
In modern times, the so-called Hindu Renaissance developed as a defense against Christian missions in India and Hinduism developed into a mission religion whch moved to the United States and other countries.
Well, enough. I need to go to work.