Lord Wellesley's Subsidiary Alliance, implemented in 1798, was a diplomatic maneuver to assert British authority over Indian princely states, avoiding direct annexation.
Under this pact, British forces were stationed within an allied Indian state for its defense against external aggression and internal unrest. The Indian ruler was obligated to finance these troops and was prohibited from forming independent alliances or engaging in warfare without British consent.
This policy substantially diminished the autonomy of Indian rulers and broadened British political dominion. Consequently, the rationale employed to legitimize the stationing of British forces was the (D) Protection of native territory by British.