There was a historical background of first Anglo-Sikh War. During the early years of nineteenth century the Sikh kingdom was expanded and amalgamated under the leadership of Ranjit Singh. At the same time the British was expanding their territory and reached up to the border of Punjab. Ranjit Singh was intelligent enough to take a dual policy. He maintained a friendship with British while on the other hand he established military army to prevent the aggression both by British and by the Afghans under Dost Mohammed Khan. He hired European and American mercenary soldiers to coach his artillery and also incorporated a large number of Hindu and Muslim armies into his force.
Ranjit Singh passed away in 1947 and almost immediate after his death his kingdom fell in a huge perturbation. His adopted son Kharak Singh was unpopular among the subjects and was expelled from power within a few months and later died in prison. His successor Nau Nihal Singh was able but he also died in a very suspicious circumstance as he was crushed by falling archway at Lahore fort while he was returning from his father's cremation. The hollow Sikh throne caused a reason for First Anglo Sikh War. Then two major factions of power Sindhanwalias and the Dogras fought over to achieve the power of Punjab. The Dogras represented an illegitimate son of Ranjit Singh named Sher Singh and put him in the throne in January of 1841. The defeated Sindhanwalas took shelter in British territory but had many followers in the Punjab army.
The Army of Punjab was expanding rapidly after Ranjit Singh's death as all the landlords and their retainers adopted arms in their hands. The army now claimed itself as 'Khalsa' or embodiment of the Sikh nation. Khalsa was the main Sikh power that took part in First Anglo Sikh War. The regimental Panchayats or committees formed a parallel source of power within the Sikh kingdom. They declared Guru Gobind Singh's ideal of Sikh commonwealth has resurrected with the Sarbatt Khalsa or the whole Sikh community attaining all executive, military and civil authority of the kingdom. The British reprobated it as 'dangerous military democracy'. British visitors and representatives reported that Khalsa army observed strict discipline and remain in a state of mutiny or rebellion against the central 'Darbar'. In a notorious instant the Khalsa force came up with riot, killing the Persians by their swords.
Sher Singh was unable to meet the demands made by Khalsa force although he maintained funds of a degenerated court. In September of 1843 a Khalsa officer named Ajit Singh Sindhanwalia assassinated Sher Singh. The Dogras took revenge and Sher Singh's widow Jind Kaur became regent of her infant son Duleep Singh. After that the officer Hira Singh was killed while attempting to attack the capital with troops under Sham Singh Attariwala. Thereby Jind Kaur's brother Jawahir Singh got the post of the Vizier in December 1844. Jawahir Singh bribed the Khalsa and promised them much wealth out of terror, which could not be made. At an army parade in September 1845 Jawahir singh was murdered in front of his sister Jind Kaur and nephew Duleep Singh.
However, the Khalsa did not take the charge of kingdom at this time. Jind Kaur publicly vowed against her brother's killer but she did nothing in action. Lal Singh became the new vizier and Tej Singh became the commander of the army. Both of them came from high class Hindu family and converted to Sikhism in 1818 as the majority of the Sikhs of Punjab at that time.
On the other hand British East India Company army also started to achieve strength after the death of Ranjit Singh and their place of action was mainly the border area of Punjab. The actions and attitudes of British were disputed under the leadership of Lord Ellenborough and later under sir Henry Hardinge. Khalsa army though had not any strong leadership became a threat to British army along the border area. Major George Broadfoot then reported about the disorder in Punjab. The main motto of East India Company was to annex the Sikh kingdom. They also were affected by the increasing tension of Punjab and Khalsa, as a result of which First Anglo-Sikh War broke out.
After the mutual demands of British East India Company were not fulfilled by the Sikh Darbar , the diplomatic relations between Sikhs and British broke. Thus first Anglo Sikh War was initiated. An English army marched towards Ferozepur, that was led by Sir Hugh Gough and accompanied by Sir Henry Hardinge, the British Governor General of Bengal. Most of the soldiers and infantry of British army came from Bengal. In response to the British Army, the Sikh army also aggressed and crossed the Sutlej River on December 11,1845. Although the commanders and many soldiers of the army were Sikhs, there were also Punjabi, Pakhtun and Kashmiri infantry units. The artillery was strongly built with heavy guns and canons.
The Sikhs claimed that they were only moving in the Sikh territory, specifically near the village of Moran on the eastern side of the river but British demanded that Sikhs had intruded in their area. So the first Anglo Sikh War was declared. The Sikh army showed no interest to surround or attack exposed English division. On December 18, Lal Singh's army clashed with British army in the Battle of Mudki and British won in a very clumsy situation. The British attacked the Sikh army on December 21. The Sikhs tried to cut off the supply line for British. Sir Harry smith was sent to face them and he won in Battle of Aliwal on January 28, 1846. Gough's main army now attacked the Sikhs at Sobrao on February 10 in the year 1846. The Sikh army was eventually trapped. This victory in the First Anglo Sikh War broke the Sikh Army.
As a result of First Anglo Sikh War the treaty was signed between British and the Sikhs, in which Sikhs had to sacrifice Kashmir and accepted a British resident at Lahore. The East India Company also had control over the Sikh Government. The Treaty also made Sikhs to give Koh-I-Noor diamond to queen Victoria.