In formal history today it is said that the vedics were aryans(which
again is a misnomer) and migrants to india through the west from central
asia thru iran and the people of IVC(indus valley civilization) were the
natives(or earliest migrants) of india and were probablu mundas(of SEAsian
origin) or dravidians who later moed south. this is purely based on linguistics
theory and doesnot have any proof. just a hypothesis.
after recent archeological, geneological and other logical discoveries
this has been completely debunked but the mystery of their origins and
identity still remains.
Ancient india even before IVC was already multi ethnic(not race). Each
ethnic group had its own faiths of which vedicism(deva worshippers), ashuraism(later
zoroastrians) and shaivaism(not the shaivism we know today but a grave
culture with lingams as tombstones or phallus worship etc) were prominent.
There were also many other cults like human idol(vishnu) worshippers,
early forms of jainism or yogic religion (as in some siddhas/yogis/recluse
sadhus) and many pagan and tribal
beliefs like animal worshipers etc.
over the time these beliefs/cultures intermingled and became hinduism
and also more outsiders(from the west mostly) came and their beliefs were
also added to this common system.
ofcourse there were also movement outside to the west especially the deva
ashura wars and ashuras moving west to iran and further west and the early
shaivites moving south.
these movements happened due to internat wars between the various kingdoms
of north india as depicted in the deva-ashura mythical wars, dasarajana
war and mahabaratha wars. devaashura mythical war of rig veda happened
in prevedic times when the rig vedics split as deva and ashura worshippers.
the deva worshippers became vedics and ashura worshippers became ashuras.
the lived in sarasvati and indus rivers respectively. dasarajana was the
second famous war(indicating a second wave) of vedicisation of some groups
of the north when the vedic baratha sudas won the war and assimilated the
won over groups into vedic religion and those that dint moved to iran.
so this time the ashuas were driven out of india who later became zoroastrians
of iran. the third major wave was the vedicisation of the shaivaites and
other southern clans like the yadus etc was during the mahabaratha times.
this was the completion of vedicisation. mot central and southers parts
were already partly vedicised before as seen in ramayana and parashurama
the deva/ashura concept was the earliest and happened sometime during
the mixing of all these original faiths and based on their belief system
some groups took to worldly and dulaistic faiths and others to sacrificial
vedic faiths. this split could have happened right during the early rig
vedic times which could have been around atleast 3-4k B.C if not earlier
and the wars continued on for another 1000 years.
the later vedic period continued with the influence of the faiths which
have already mingled and hence we see shiva(early form as in rudra, shiva
the benevolent etc) and vishnu mentioned from later rig and yejur veda
onwards. thus the concepts of vedas itself is a mix of all these faiths
and made by priests from all these clans(hence we have so many ghotras
and the 7 saptha rishis must have been each from each one of these clans
or ethnic groups)