Short answers, pulled from the story.
The Buddha claimed to recall ninety-one eons of past lives on the night he attained awakening. This memory anchors rebirth as a core teaching alongside karma and nirvana within early Buddhist texts like the Majjhima Nikaya.
Traditional cosmology divides existence into six realms known as gati including three good realms of deva gods, asura demigods, and human beings. Three evil realms consist of animals, ghosts, and hellish states determined by good or bad karma.
Indian Buddhist schools split over whether an intermediate state exists after death with Sarvastivada accepting antarabhava doctrine while Theravada rejected it favoring immediate leap. Vasubandhu defended intermediate existence in Abhidharmakosha arguing beings arise at death place before conception.
Ancient Buddhists cited direct knowledge gained through parapsychological abilities called abhinna such as special yogic perception verifying truth empirically. Modern authors point near-death experiences past-life regression xenoglossy as evidence supporting these claims.
Buddhism assumes no soul contrasting Brahmanical belief eternal essence identical Brahman regarding reincarnation mechanisms. Jainism accepts Jiva soul involved mechanism karmic particles stick determining next birth while Buddhism focuses on causal links without permanent self.