The Treaty of Amritsar of 25 April 1809 fixed the Sutlej as the boundary between Ranjit Singh Ji's state and the East India Company. He gave up his claims east of the river. The Cis-Sutlej chiefs, Patiala, Nabha, Jind, Kaithal, Faridkot and the rest, came under British protection.
He signed because a British force under David Ochterlony was on the river and because he judged the fight not worth it. He then turned west and spent thirty years taking Multan, Kashmir, Peshawar and the frontier instead.
The treaty is the reason Punjab was divided long before 1947. Everything east of the Sutlej developed under direct or indirect British rule from 1809, everything west under the Lahore state until 1849. The two halves had different revenue systems, different armies and different law for forty years.
The Phulkian states owe their survival to it. Ludhiana became a British cantonment because of it. Phillaur fort was built to look across it.
It held for thirty-six years. The Khalsa army crossed the Sutlej in December 1845 and the First Anglo-Sikh War followed.
The negotiation was conducted for the Company by Charles Metcalfe, who was twenty three, and who followed the Maharaja's camp across the Malwa for months before terms were reached. A clash between Akalis and his escort at Amritsar during Muharram is part of the standard account of that winter.
It ended the possibility of a single Sikh state covering the whole Punjab, and the Malwa and the Majha have had different political histories ever since because of it.
A political agency was set up at Ludhiana to watch the line, and its correspondence with Lahore is one of the fuller records of the Sikh state written from outside it. Shah Shuja and other Afghan exiles were lodged there on British protection while the arrangement lasted.