Explanation:

Here's the breakdown:

- The Treaty of Sagauli was signed in 1815–1816, right after the Anglo-Nepalese War.

- It was signed between the British East India Company and the Gurkhas (Nepal Kingdom).

- The treaty forced Nepal to cede a huge chunk of territory—like Sikkim, Kumaon, and Garhwal—to the British.

- Option 2, the Nawab of Bengal, had no part in this treaty. The Bengal Nawab's power was already gone after 1757 (Battle of Plassey).

- Option 3, the Nawab of Awadh, wasn't involved in this either; though the British did sign treaties with them, Sagauli wasn't one of them.

- Option 4, Marathas—also incorrect. Their rivalry with the British was handled through other treaties (like the Treaty of Bassein).

So, long story short: the right answer is Option 1: Gurkhas.