The Brahmo Samaj experienced another phase of energy, when Keshab Chandra Sen (1838-1884) was made the acharya by Debendranath Tagore soon after the former joined the Samaj in 1858.  

• Keshab (also spelt Keshub) was instrumental in popularising the movement, and branches of the Samaj were opened outside Bengal—in the United Provinces, Punjab, Bombay, Madras and other towns. 

• Unfortunately, Debendranath did not like some of Sen’s ideas which he found too radical, such as cosmopolitanisation of the Samaj’s meetings by inclusion of teachings from all religions and his strong views against the caste system, even open support to inter-caste marriages.  
• Keshab Chandra Sen was dismissed from the office of acharya in 1865. Keshab and his followers founded the Brahmo Samaj of India in 1866, while Debendranath Tagore’s Samaj came to be known as the Adi Brahmo Samaj. 
• In 1878, Keshab’s inexplicable act of getting his thirteen-year-old daughter married to the minor Hindu Maharaja of Cooch-Behar with all the orthodox Hindu rituals caused another split in Keshab’s Brahmo Samaj of India.  
• Earlier, Keshab had begun to be considered as an incarnation by some of his followers, much to the dislike of his progressive followers. Further, Keshab had begun to be accused of authoritarianism. 
• After 1878, the disgusted followers of Keshab set up a new organisation, the Sadharan Brahmo Samaj.  

• The Sadharan Brahmo Samaj was started by Ananda Mohan Bose, Shibchandra Deb and Umesh Chandra Datta.  
• It reiterated the Brahmo doctrines of faith in a Supreme Being, one God, and the belief that no scripture or man is infallible, belief in the dictates of reason, truth and morality. 

Source: Spectrum’s A Brief History of Modern India.