Explanation:

Civilians, in the majority Sikhs, had assembled to participate in the annual Baisakhi celebrations, a religious and cultural festival for Punjabi people and also to condemn the arrest and deportation of two national leaders, Satya Pal and Dr Saifuddin Kitchlew. Coming from outside the city, many may have been unaware of the imposition of martial law.
The Jallianwala Bagh massacre took place on 13 April 1919 when troops of the British Indian Army under the command of Colonel Reginald Dyer fired machine guns into the crowd.Both the Defence of India Act and Rowlatt Act were in force then, but the Rowlatt Satyagraha was launched by Gandhiji (not by the assembly at Jallianwala).