Why did India's constitution outlaw caste discrimination?

Because caste had long meant oppression for millions of people, and one of them helped write the rules of the new country. After independence in 1947, India banned discrimination on the basis of caste through its constitution: Article 15 prohibits it, and Article 17 declared the practice of untouchability illegal. A key figure in drafting that constitution, B. R. Ambedkar, had himself been born into a caste classified as untouchable.

Caste works on two levels. An ancient framework called varna sorts people into four broad classes: Brahmins (priests), Kshatriyas (rulers and warriors), Vaishyas (artisans, merchants and farmers) and Shudras (labourers). Outside it sit the Dalits, once called "Untouchables", and the Adivasis, India's tribal peoples, who were oppressed, marginalised and persecuted. Beneath the four varnas are thousands of jatis, smaller groups within which people have normally been expected to marry. The British Raj furthered the system through census classifications and preferential treatment for Christians and certain castes.

Ambedkar became a leader of human-rights campaigns. In 1932, when a British award gave Dalits separate electoral representation, Mahatma Gandhi went on a hunger strike against it, arguing it would split the Hindu community into two groups; Ambedkar later called the fast a form of coercion. Their compromise, the Poona Pact, saw Gandhi end his fast and Ambedkar drop his demand for a separate electorate.

The ban changed the law, not the whole society. An estimated 98 percent of Indians, across religions, still identify with a caste, and caste-based discrimination, segregation, violence and inequality persist: a 2005 UN report counted about 31,440 violent acts against Dalits reported in 1996 alone.