From the time that European explorers and traders landed in Africa in the 17^th century, a slave trade began. Black people were captured and brought from Africa to America, sold to white planters, and made to work on cotton and other plantations, most of them in the southern united states. In the plantations, they were made to work long hours, typically from dawn to dusk, punished for "inefficient work" and whipped and tortured.

Political leaders and social reformers like Jyotirao Phule, Gandhiji, BR Ambedkar and EV Ramaswamy Naicker advocated and worked to establish a society in which caste inequalities are absent.
Partly due to their efforts and partly due to other socio-economic changes, caste and caste system in modern India have undergone great changes.
But these assertions did not go unchallenged. Orthodox Hindu society also reacted by founding Sanatan Dharma Sabhas, Bharat Dharma Mahamandal, Brahman Sabha etc.
The object of these associations was to uphold caste distinctions as a cornerstone of Hinduism and show how this was supported by the scriptures.
Thus, debates and struggles over caste continued beyond the British period and still remain a controversial issue today.
I think 'The Temple Entry Movement' started by BR Ambedkar was the most important movement against caste in colonial times. Ambedkar led three such movements for temple entry between 1927 and 1935.

An account of the discussion:
Girls were not allowed the access to education.
Fundamentalists opposed her.
She opened muslim girls schools at Patna and Calcutta.
Madame Rokeya Hossain opposed this dictum and advocated for girl education.

(i) Women were married at an early age.
(ii) Women were forced to burn themselves on the funeral pyre of their husbands. Woman who died in this manner, whether willing or otherwise, were called Sati which meant virtuous women.
(iii) Women's right to property were also restricted.
(iv) Women had virtually no access to education. In many parts of the country, people believed that if a woman was educated, she would become a widow.

(i) Jyotiba Phule argued that the Aryans were foreigners, who came from outside the subcontinent and defeated and subjugated the true children of the country, those who had lived here from before the coming of the Aryans.
(ii) As the Aryans established their dominance, they began looking at the defeated population as inferior, as low-caste people. According to Phule, the upper caste had no right to their land and power. In reality, the land belonged to indigenous people, and so-called low castes.
(iii) Phule claimed that before Aryan rule, there existed a golden age, when warriors and peasants tilled the land and ruled the Maratha countryside in just and fair ways.