Jallianwala Bagh massacre: British Indian Army troops led by Brigadier-General Reginald Dyer kill approximately 379–1,000 unarmed demonstrators including men and women in Amritsar, India; and approximately 1,500 injured.

The Jallianwala Bagh massacre, also known as the Amritsar massacre, took place on 13 April 1919. A large crowd had gathered at the Jallianwala Bagh in Amritsar, Punjab, British India, during the annual Baisakhi fair to protest against the Rowlatt Act and the arrest of pro-Indian independence activists Saifuddin Kitchlew and Satyapal. In response to the public gathering, the temporary brigadier general R. E. H. Dyer surrounded the people with his Gurkha and Sikh infantry regiments of the British Indian Army. The Jallianwala Bagh could only be exited on one side, as its other three sides were enclosed by buildings. After blocking the exit with his troops, Dyer ordered them to shoot at the crowd, continuing to fire even as the protestors tried to flee. The troops kept on firing until their ammunition was low and they were ordered to stop. Estimates of those killed vary from 379 to 1,500 or more people; over 1,200 others were injured, of whom 192 sustained serious injury. Britain has never formally apologised for the massacre but expressed "deep regret" in 2019.

The Indian Army during British rule, also referred to as the British Indian Army, was the main military force of India until national independence in 1947. Formed in 1895 by uniting the three Presidency armies, it was responsible for the defence of both British India and the princely states, which could also have their own armies. As stated in the Imperial Gazetteer of India, the "British Government has undertaken to protect the dominions of the Native princes from invasion and even from rebellion within: its army is organized for the defence not merely of British India, but of all possessions under the suzerainty of the King-Emperor." The Indian Army was a vital part of the British Empire's military forces, especially in World War I and World War II.

Colonel Reginald Edward Harry Dyer, was a British military officer in the Bengal Army and later the newly constituted British Indian Army. His military career began in the regular British Army, but he soon transferred to the presidency armies of India.