The Third Anglo-Afghan War (also referred to as the Third Afghan War) began on 6 May 1919 and ended with an armistice on 8 August 1919. Whilst it was essentially a minor tactical victory for the British in so much as they were able to repel the regular Afghan forces, in many ways it was a strategic victory for the Afghans. For the British, the Durand Line was reaffirmed as the political boundary between Afghanistan and British India and the Afghans agreed not to foment trouble on the British side. The Afghans finally won the right to conduct their own foreign affairs as a fully independent state.
The end of the Second Afghan War in 1880 marked the beginning of almost forty years of reasonably good relations between Britain and Afghanistan under the leadership of Abdurrahman and Habibullah, during which time the British attempted to manage Afghan foreign policy through the payment of a large subsidy. Ostensibly, the country remained independent, however, under the Treaty of Gandamak (1879) it was accepted that in regards to external matters it would "have no windows looking on the outside world, except towards India".
The death in 1901 of Amir Abdurrahman led indirectly to the war that began eighteen years later. His successor, Habibullah, was an unreliable and unstable leader who alternately sided with Britain and Russia according to whoever paid the highest price. Despite feeling considerable resentment over not being consulted over the Anglo-Russian Convention of 1907 (Convention of St. Petersburg), Afghanistan remained neutral during the First World War (1914–1918), resisting considerable pressure from the Ottoman Empire when it entered the conflict on the side of Imperial Germany and the Sultan (the titular leader of Islam), called for a jihad against the Allies.
Upon seizing the throne, Amanullah had his brother Nasrulla arrested for their father’s murder and had him sentenced to life imprisonment. Nasrulla had been the leader of a more conservative element in Afghanistan and his treatment rendered Amanullah’s position as Amir somewhat tenuous. By April 1919 he realised that if he could not find a way to placate the conservatives he would be unlikely to maintain his hold on power. Looking for a diversion from the internal strife in the Afghan court and sensing advantage in the rising civil unrest in India following the Amritsar massacre Amanullah decided to invade British India.