PM Modi took on twitter to pay tribute to Jallianwala Bagh Massacre martyrs, he wrote “I recall the sacrifices of all those martyred on this day in Jallianwala Bagh, Their great sacrifice inspires us to work even harder to fulfil the dreams of our great freedom fighters and build a strong and developed India.”
The Jallianwala Bagh Massacre occurred when General Dyer ordered troops to open fire on a large peaceful mob gathering to oppose the Rowlatt Act. 
The Rowlatt Act was a contentious piece of law enacted by the British colonial government in 1919 that authorised the government to arrest and hold Indians without trial, prompting massive demonstrations and agitation across the country.