Change in caste system in later vedic period

Explanation:

It is said that the caste system in the Rig Vedic times was based on occupations of the people and not on birth. Change of caste was common. ... But in the later Vedic period it became rigid when the Brahmins and the kshatriyas became powerful and the vaishyas were made to pay tributes.

sumerians were responsible.

the hyksos invasion. the hyksos were able to attack egypt successfully because of their skills in using bronze weapons, composite bows and the use of the horse and chariot during the invasion. although the egyptians depict a barbarian-type overthrow, the truth is the seizure was likely a relatively peaceful one.