The question asks about a specific social reform supported by the British through the Regulation Act of 1829, driven by the efforts of Raja Ram Mohan Roy. This Act marked a significant step in social reform in British India.
Raja Ram Mohan Roy was a prominent social and religious reformer of the 19th century. He was deeply concerned about various social evils prevalent in Hindu society. He strongly believed in rationalism and the need to reform existing practices based on principles of human dignity and justice. His efforts were crucial in bringing about significant legislative changes.
The practice of Sati (or Suttee) involved the tradition where a widow immolated herself, either voluntarily or by coercion, either on her deceased husband's funeral pyre or shortly thereafter. This practice was deeply entrenched in certain sections of society, often justified through misinterpretations of religious texts.
Raja Ram Mohan Roy campaigned vigorously against the practice of Sati. He presented petitions and arguments to the British authorities, highlighting the cruelty and inhumanity of the practice. His advocacy, coupled with the support of Governor-General Lord William Bentinck, led to the enactment of the Regulation Act of 1829 (also known as the Bengal Sati Regulation). This Act officially declared the practice of Sati illegal and punishable by law in the Bengal Presidency. It was later extended to other parts of British India.
Therefore, the social reform supported by the British through the Regulation Act of 1829 at the initiative of Raja Ram Mohan Roy was the Abolition of Sati.