Short answers, pulled from the story.
Ali Mohammed Khan founded the Kingdom of Rohilkhand in 1721. He was an orphaned Jat boy adopted into the Barech tribe who carved out a kingdom from the crumbling remains of the Mughal Empire after the death of Emperor Aurangzeb.
The internal collapse of the Kingdom of Rohilkhand was triggered by the betrayal of Hafiz Rehmat Khan in 1749. Hafiz Rehmat Khan and his allies broke their sacred oath to protect Ali Mohammed Khan's six sons and usurped the most valuable portions of the territory for themselves.
The First Rohilla War ended the independent Kingdom of Rohilkhand on the 23rd of April 1774. The decisive confrontation occurred at the Battle of Miranpur Katra where the Rohillas under Hafiz Rahmat Ali Khan were defeated by Colonel Alexander Champion.
Faizullah Khan, the eldest surviving son of Ali Mohammed Khan, signed a treaty with the British to establish the princely state of Rampur on the 7th of October 1774. This treaty was signed in the presence of British Commander Colonel Champion and ensured the dynasty continued to rule under British protection.
The Nawab of Oudh annexed the Kingdom of Rohilkhand in 1773 because the Rohillas were unable to repay the massive debt incurred for military support against the Marathas. The Nawab of Oudh, Shuja-ud-Daula, appealed to Warren Hastings for assistance and promised a sum of forty lakhs of rupees in return for military support.