The First Anglo-Afghan War (Pashto: د افغان او انگرېز لومړی جنگ; Persian: جنگ اول افغان و انگلیس) was fought between the British Empire and the Emirate of Kabul from 1838 to 1842. The British initially successfully invaded the country taking sides in a succession dispute between emir Dost Mohammad Khan (Barakzai) and former King Shah Shujah (Durrani), whom they reinstalled upon occupying Kabul in August 1839. The main British Indian force occupied Kabul and endured harsh winters. The force and its camp followers were almost completely massacred during its 1842 retreat from Kabul.

The British then sent what was widely termed an "Army of Retribution" to Kabul to avenge the destruction of the previous forces. After recovering prisoners, they left Afghanistan by the end of the year. Dost Mohammed returned from exile in India to resume his rule.

It was one of the first major conflicts during the Great Game, the 19th century competition for power and influence in Central Asia between Britain and Russia.

The 19th century was a period of diplomatic competition between the British and Russian empires for spheres of influence in South Asia known as the "Great Game" to the British and the "Tournament of Shadows" to the Russians. With the exception of Emperor Paul (whose 1800 order to invade India was cancelled after his assassination in 1801), no Russian tsar ever seriously considered invading India. However, for most of the 19th century, Russia was viewed as "the enemy" in Britain; any Russian advance into Central Asia, into what is now Kazakhstan, Turkmenistan, Kyrgyzstan, Uzbekistan and Tajikistan, was always assumed (in London) to be directed towards the conquest of India, as the American historian David Fromkin observed, "no matter how far-fetched" such an interpretation might be. In 1832, the First Reform Bill lowering the franchise requirements to vote and hold office in the United Kingdom was passed, which the ultra-conservative Emperor Nicholas I of Russia openly disapproved of, setting the stage for an Anglo-Russian "cold war", with many believing that Russian autocracy and British democracy were bound to clash. In 1837, Lord Palmerston and John Hobhouse, fearing the instability of Afghanistan, the Sindh, and the increasing power of the Sikh kingdom to the northwest, raised the spectre of a possible Russian invasion of British India through Afghanistan. The British tended to misunderstand the foreign policy of the Emperor Nicholas I as anti-British and intent upon an expansionary policy in Asia; whereas in fact though Nicholas disliked Britain as a liberal democratic state that he considered to be rather "strange", he always believed it was possible to reach an understanding with Britain on spheres of influence in Asia, believing that the essentially conservative nature of British society would retard the advent of liberalism. The main goal of Nicholas's foreign policy was not the conquest of Asia, but rather upholding the status quo in Europe, especially by co-operating with Prussia and Austria, and in isolating France, as Louis Philippe I, the King of the French was a man whom Nicholas hated as an "usurper". The duc d'Orleans had once been Nicholas's friend, but when he assumed the throne of France after the revolution of 1830, Nicholas was consumed with hatred for his former friend who, as he saw it, had gone over to what he perceived as the dark side of liberalism. The idea that Russia was a threat to the East India Company is one version of events. Scholars now favour a different interpretation that the fear of the East India Company was in fact the decision of Dost Mohammed Khan and the Qajar Ruler of Iran to form an alliance and extinguish Sikh rule in Punjab. The British feared that an invading Islamic army would lead to an uprising in India by the people and princely states therefore it was decided to replace Dost Mohammed Khan with a more pliant ruler. "Rumours could cost lives and Empire itself. Therefore instead of fixating on the oriental other, the East India Company played up the threat of the Russian bear".

In 1834, Shah Shuja Durrani invaded Kandahar with the aid of the British, but was defeated.

The Company sent an envoy to Kabul to form an alliance with Afghanistan's Amir, Dost Mohammad Khan against Russia. Amidst the Afghan civil war, the Sikhs seized Peshawar from the Peshawar sardars and subjugated them. The British feared the Dal Khalsa, and they considered the Sikh army to be a far more formidable threat than the Afghans who did not have a well-disciplined army, instead of having only a tribal levy where under the banner of jihad tribesmen would come out to fight for the Emir. For this reason, Lord Auckland preferred an alliance with the Punjab over an alliance with Afghanistan. The British could have had an alliance with the Punjab or Afghanistan, but not both at the same time.

When Governor-General of India Lord Auckland heard about the arrival of Russian envoy Count Jan Prosper Witkiewicz (better known by the Russian version of his name as Yan Vitkevich) in Kabul and the possibility that Dost Mohammad might turn to Russia for support, his political advisers exaggerated the threat. Alexander Burnes, the Scotsman who served as the East India Company's chief political officer in Afghanistan, described Witkiewicz: "He was a gentlemanly and agreeable man, of about thirty years of age, spoke French, Turkish and Persian fluently, and wore the uniform of an officer of the Cossacks". The presence of Witkiewicz had thrown Burnes into a state of despair, leading one contemporary to note that he "abandoned himself to despair, bound his head with wet towels and handkerchiefs and took to the smelling bottle". Dost Mohammad had in fact invited Count Witkiewicz to Kabul as a way to frighten the British into making an alliance with him against his archenemy Ranjit Singh, the Maharaja of the Punjab, not because he really wanted an alliance with Russia. The British had the power to compel Singh to return the former Afghan territories he had conquered whereas the Russians did not, which explains why Dost Mohammad Khan wanted an alliance with the British. Burnes wrote home after having dinner with Count Witkiewicz and Dost Mohammad in late December 1837: "We are in a mess home. The emperor of Russia has sent an envoy to Kabul to offer...money [to the Afghans] to fight Rajeet Singh!!! I could not believe my own eyes or ears." On 20 January 1838, Lord Auckland sent an ultimatum to Dost Mohammad telling him: "You must desist from all correspondence with Russia. You must never receive agents from them, or have aught to do with them without our sanction; you must dismiss Captain Viktevitch [Witkiewicz] with courtesy; you must surrender all claims to Peshawar". Burnes himself had complained that Lord Auckland's letter was "so dictatorial and supercilious as to indicate the writer's intention that it should give offense", and tried to avoid delivering it for long as possible. Dost Mohammad was indeed offended by the letter, but in order to avoid a war, he had his special military advisor, the American adventurer Josiah Harlan, engage in talks with Burnes to see if some compromise could be arranged. Burnes in fact had no power to negotiate anything, and Harlan complained that Burnes was just stalling, which led to Dost Mohammad expelling the British diplomatic mission on 26 April 1838.

British fears of a Persian and Afghan invasion of India took one step closer to becoming a reality when negotiations between the Afghans and Russians broke down in 1838. The Qajar dynasty of Persia, with Russian support, attempted the Siege of Herat. Herat, in Afghanistan, is a city that had historically belonged to Persia; the Qajar shahs had long desired to take it back. It is located in a plain so fertile that is known as the "Granary of Central Asia"; whoever controls Herat and the surrounding countryside also controls the largest source of grain in all of Central Asia. Russia, wanting to increase its presence in Central Asia, had formed an alliance with Qajar Persia, which had territorial disputes with Afghanistan as Herat had been part of the Safavid Persia before 1709. Lord Auckland's plan was to drive away the besiegers and replace Dost Mohammad with Shuja Shah Durrani, who had once ruled Afghanistan and who was willing to ally himself with anyone who might restore him to the Afghan throne. At one point, Shuja had hired an American adventurer - Josiah Harlan - to overthrow Dost Mohammad Khan, despite the fact Harlan's military experience comprised only working as a surgeon with the East India Company's troops in the First Burma War. Shuja Shah had been deposed in 1809 and had been living in exile in British India since 1818, collecting a pension from the East India Company, which believed that he might be useful one day. The British denied that they were invading Afghanistan, claiming they were merely supporting its "legitimate" Shuja government "against foreign interference and factious opposition." Shuja Shah by 1838 was barely remembered by most of his former subjects and those that did viewed him as a cruel, tyrannical ruler who, as the British were soon to learn, had almost no popular support in Afghanistan.