Sage Kashyapa had many wives. Among them were the sisters Diti and Aditi. The sons of Aditi were virtuous and called Devas (meaning the gods or the celestials.) The sons of Diti were wicked by nature and were called the Asuras ( meaning the demons.) There were frequent wars between the Devas and the Asuras and the Asuras lost all the battles.
After having been defeated repeatedly, the Asuras lost their kingdom in the heaven and were also stripped of their sovereignty. Using their powers, the Asuras got themselves reincarnated on the earth. They were born into various forms like human beings and animals. They began to oppress all kinds of people causing them immense hardship. They also harassed the rishis (sages) and obstructed their penances and other rituals.
Mother Earth, finding it unable to withstand the burden created by the oppressive acts of the Asuras went to Brahma, the Creator and pleaded with him to ease her burden. Brahma assured her that he would ask the Devas to come to her help. Accordingly, Brahma commanded the Devas to take birth on the earth, confront the Asuras and eliminate them eventually.
The Devas accepted the command of Brahma. Then they went to Vaikunta, the abode of Lord Vishnu (Narayana), the God of all gods and the destroyer of evil and requested Him that he should also become incarnate on the earth. Vishnu acceded to their prayer. They discussed with Vishnu on the parts they have to play on the earth. The Devas were born in the race of sages. Eventually, they destroyed the Asuras completely and made the earth a safe place to live.
Sage Vaisampayana narrates the names of all those born on the earth as per Brahma's command. Since the list is too long, I am not giving the names here. Knowing these names may not be necessary to understand the story of Mahabharata.