After the First World War, the Triveni Sangh was formed by

The Triveni Sangh was a significant caste-based political coalition and social reform movement formed in April 1933 in the Shahabad district of Bihar. It was established to represent the interests of the 'middle peasant castes' against the dominance of upper-caste groups like Bhumihars and Rajputs. The 'Triveni' (meaning three streams) represented the coming together of three major intermediary backward castes: the Ahirs (Yadavs), Kurmis, and Koeris. Its founders included leaders like Sardar Jagdev Singh Yadav, Shivpujan Singh, and J.N.P. Mehta. The movement sought to provide political solidarity for these 'true peasants' (Sachhe Kisan) and contested the 1937 provincial elections. While the options provided in the question use 'Ahirs' and 'Yadavs' interchangeably in historical literature, the specific combination of Ahirs and Kurmis (along with Koeris) defines the Sangh's core identity.

Sources

1. [1] https://en.wikipedia.org/wiki/Triveni_Sangh