Read it without any addition and you will see what I think it is saying. Plainly, what the writer wrote. No more, no less.
But, if you want me to engage in the exercise of taking knowledge of some historical event and cramming it into the scripture so I can say "aha! The bible is literally correct!" I certainly can. It will be no closer to the actual context of the scripture than you get, but it can be done in numerous ways.
Gen. 6:2That the sons of God (Spaniards[who were technologically more advanced, coming from the Old World]) saw the daughters of men (Aztecs[the primitive people of less sophistication]) , they took them wives of all which they chose(raped and plundered, even their women, with no discretion, because of their dominance).
Gen. 6:4 There were giant (ships bringing many from the Old World) , in the earth (New World) in those days(do I really need to give an explanation here?); and also after that(the Spanish Inquisition), when the sons of God (Spaniards, bearing the testimony of Christ) came in unto the daughters of men (pagan Aztecs), and they bare children to them, the same became mighty men (Spanish speaking natives with knowledge of Truth) which were of old, men of renown(Catholics).
Pretty easy, actually. One culture overcoming and dominating another is no one-time event. This story is told many tmes. But you missed the whole point because you were trying to give a specific form to a universal struggle facing all tribes and nations.