The war lasted from December 1845 to March 1846, ending with the Treaty of Lahore on 9 March, and was fought chiefly in four battles: Mudki on 18 December, Ferozeshah on 21 and 22 December, Aliwal on 28 January and Sobraon on 10 February, with a smaller engagement at Baddowal on 21 January.
The Khalsa army crossed the Sutlej on 11 December. Its commander, Tej Singh, and the wazir, Lal Singh, were both in communication with the British before and during the fighting. At Ferozeshah, with the British position broken and out of ammunition overnight, Tej Singh withdrew a fresh force that could have finished it.
British accounts of Ferozeshah are frank about how close it was. Officers burned papers. The line spent the night in the open expecting to be destroyed at dawn.
Aliwal, fought by Harry Smith against Ranjodh Singh Majithia, is studied in staff colleges as a model action. Sobraon was a massacre at the bridgehead.
The Treaty of Lahore on 9 March 1846 took the Jalandhar Doab, imposed an indemnity, reduced the army and installed a British Resident. Kashmir was sold a week later. The state survived for three more years as a protectorate.
The Khalsa army had been the political power at Lahore since 1839, with regimental panchayats negotiating directly with the court. Sending it across the Sutlej was as much a way of getting it out of the capital as it was a campaign.
The Sikh army was not beaten in the field so much as sold. The conduct of its commanders, Lal Singh and Tej Singh, is described in almost every account as deliberate betrayal.
Henry Lawrence took the Residency and the Lahore government continued in name for three more years under a Resident who signed its orders. The annexation of 1849 was the second act of one process.