With Vichitravirya having died of sickness, Bhishma unable to take the throne because of his vow, and Bahlika’s line unwilling to leave Bahlika Kingdom, there was a succession crisis in Hastinapur. Satyavati invites her son Vyasa toimpregnate the queens Ambika and Ambalika under the Niyoga practice. When Vyasa went to impregnate Ambika, his scary appearance frightened her, so she closed her eyes during their union; hence, her son was born blind.
Dhritarashtra, along with his younger half-brother Pandu is trained in the military arts by Bhishma and Kripacharya. Hindered by his handicap, Dhritarashtra is unable to wield weapons, but has the strength of one hundred thousand elephants due to boon given by Vyasa, and is said to be so strong that he can crush iron with his bare hands.
When it came time to nominate an heir, Vidura suggested that Pandu would be a better fit because he was not blind. Though bitter at the result, Dhritarashtra willingly conceded the crown, though this act would flower into the protectiveness he would have over his crown later in life. Dhritarashtra marries Gandhari of Hastinapur’s weakened and lowly vassal covers Gandhar. Gandhari her eyes with cloth in order to better understand her husband’s blindness. He and Gandhari had one hundred sons, called the Kauravas and one daughter Dushala. He also had a son named Yuyutsu with a concubine.
Lord Krishna as a peace emissary of Pandavas traveled to Hastinapura persuading Kauravas to avoid bloodshed of their own kin. However, Duryodhana conspired to arrest him that resulted in failure of the mission. After Krishna’s peace mission failed and the war seemed inevitable, Vyasa approached Dhritarashtra and offered to grant him divine vision, so that Dhritarashtra could see the war. However, not willing to see his kin slaughtered, Dhritarashtra asked that the boon be given to Sanjaya his charioteer. Sanjaya dutifully narrates the war to his liege, reporting how Bhima killed all his children. Sanjaya would console the blind king while challenging the king with his own viewpoints and morals. When Lord Krishna displayed his Vishvarupa (Universal Form) to Arjuna on the battlefield of Kurukshetra, Dhritarashtra regretted not possessing the divine sight.
Dhritarashtra was confident that Bhishma, Drona, Karna and other invincible warriors would make the Kauravas camp victorious. He rejoiced whenever the tide of war turned against the Pandavas. However, the results of the war devastated him. All of his trueborn sons were killed in the carnage. Dhritarashtra’s only daughter Duhsala was widowed. Yuyutsu had defected to Pandava side at the onset of war and was the only son of Dhritrashtra who had managed to survive Kurukshetra War.
Dhritarashtra was furious with Bhima for mercilessly slaying all his sons, especially Duryodhana. After the war ended, the victorious Pandavas arrived at Hastinapur for the formal transfer of power. The Pandavas go to embrace their uncle and give their respects. Dhritarashtra hugged Yudhishtria heartily. When Dhritarashtra turned to Bhima, Lord Krishna sensed the danger and asked Bhima to move Duryodhana’s iron statue of Bhima (used by the prince for training) in his place. Dhritarashtra crushed the statue into pieces, and then broke down crying, his anger leaving him. Broken and defeated, Dhritarashtra apologized for his folly and wholeheartedly embraced Bhima and the other Pandavas.
It is about why Dhritarashtra was blind by birth.
Dhritarashtra was a hunter, many lives ago. One fine day, he wilfully blinded a parent duck through his arrows who was crossing a river and simultaneously killed 100 baby ducks. In subsequent lives, he did good karma so in his 100th life, he was born blind as a king and all his 100 sons were brutally killed in the war when he sided with Adharma during the war of Mahabharat.