The two hundred Angels that followed the Archangel Azazel to Eth to live with free will amongst the newly isolated (following the fall of the First Kree Empire) Kree of Earth taking wives as they wished.
As warned the Nephilim's arrogance and self proclaimed superiority soon fell in to debauchery, debasement, and exploitation and war with the Kree city of Tara-Ka followed.
In this catacysmic war, as the might of the Nephilim was matched with the technology and magics of the Kree, the Earth was all but ruined, with entire continents shifting, including the movement of Tara-Ka to what is now known as the South Pole, saved only by it's technologies and magic.
Observing this the Lord of Eth, Nulr, took action due to the unnatural imbalance caused by the actions of the Fallen Angels. The Nephilim were banished to the world of Sheol in Hel and the earth was flooded and then plunged into an ice age in order to heal, not to emerge for millenia.
The Nephilim are now fully the creatures of Hel, steeped in resentment, hate, and jealousy of the people of Earth, a world they see rightfully as theirs and will one day reclaim.