The first Indian ruler who joined the Subsidiary Alliance was

The first Indian ruler to enter into Lord Wellesley’s Subsidiary Alliance was the Nizam of Hyderabad. Wellesley concluded the inaugural subsidiary treaty with the Nizam in 1798, requiring the dismissal of French-trained troops and the maintenance of a British subsidiary force in return for Company protection; a subsequent 1800 treaty further increased the subsidiary force and led to territorial cessions by the Nizam [1]. Contemporary accounts and summaries list the Nizam (1798) as the first to accept the system, followed by Mysore (1799), Awadh (1801) and the Peshwa (treaty of Bassein, 1802), confirming that other major Indian rulers joined only after Hyderabad’s agreement [2].

Sources

1. [1] Modern India ,Bipin Chandra, History class XII (NCERT 1982 ed.)[Old NCERT] > Chapter 4: The British Conquest of India > Expansion under Lord Wellesley (1798-1805) > p. 78
2. [2] Rajiv Ahir. A Brief History of Modern India (2019 ed.). SPECTRUM. > Chapter 5: Expansion and Consolidation of British Power in India > States which Accepted Alliance > p. 122