Kurukshetra |
The Pandavas and the Kauravas are both descended from the same ancestor, Kuru. Both Dhritarashtra and Pandu were brothers and belonged to the same Kuru clan. The descendants of Kuru were Kuruvanshis which in due course of time, became Kauravas.
Technically speaking, non of the children of Dhritharastra or Pandu, were biologically Kurus. The last of the Kauravas were Bhisma, Chithrangadha, and Vichitraveerya. Bhishma had sworn to brahmacharya, Chitrangada died childlessly so did Vichithraveerya, thus ending the biological Kuru clan.
Vedic dharma sanctions a childless couple (if the male is incapable of having children) to beget a child through a sibling of the male or a Rishi/Sanyasi, with the consent of the husband. This applies to a widow too. She has the option to remarry, if she wishes not to, she can get a child in the same method by her choice and society accepts them as the legal children of her husband.
In this story, after the demise of her sons, Sathyavathi asks Beshma to marry he refuses to stick to his oath of staying unmarried and brahmacharya. It is then she approaches her firstborn Krishna Dwaipaya (vedayasa). So though Dhritarashtra and Pandu were fathered by Vedhavyasa (their father's, half-brother, son of Satyavati and sage Parasara ) are considered legal. Therefore known as KURUS.
Kuru Vansh |
Vedic Dharma does not permit a BLIND man to be a king, hence Pandu was made the king of Hastinapur, and when Pandu relinquished the throne, Dhritharastra was nominated the ACTING KING, in place of his brother Pandu.
Though Pandu was the original ruler, after the curse from a sage, that he would never be able to enjoy the pleasure of married life, he renounced the throne and let his brother Dhritarashtra become the king. Since Dhritarashtra, was the ruler of the Hastinapur, he was considered the rightful heir of the Kuruvansh, and his sons were called as Kauravas.
If Pandu did not get children, then alone his children were entitled to the throne, but it so happened, Pandu did get children by the means sanctioned by the Vedic dharma, therefore his children were the legal heir to the throne of Hastinapura.
The Pandavas get their name from being the sons of Pandu, also the fact that their father was not the ruler of Hastinapur, they were considered as the outsiders and when they came to Hastinapura (after the death of their father) people for the sake of identification among the hundred and five KAURAVAS called them Pandavas which stuck on to the FIVE brothers for eternity.
The division deepened, with Duryodhan's jealousy of them, and his constant plots to eliminate them, which culminated in the burning of the Lac house and then Draupadi Swayamvar. With the Pandavas, later making their own capital at Indraprastha, the difference between them and the Kauravas deepened even more.
In the epic battle, the whole clan was fighting together against Pandu's sons. So to differentiate, Pandavas's sons were called Pandavas, and the other side was Kauravas. Thus, pandavas were also kouravas.