Why did Gandhi ji call off …

1)  Gandhiji launched nationwide satyagraha against Rowlatt Act in 1919. This Act had been hurriedly passed despite the united opposition of Indian members. 
2)  This Act gave the government enormous powers to repress political activities, and allowed detention of political prisoners without trial for two years. 
3)  Rallies were organized in various cities, workers went on strike in railway workshops, and shops closed down. 
4)  Alarmed by the popular upsurge, and scared that lines of communication such as telegraph and railways would be disrupted, the British administration decided to clamp down on nationalists. 
5)  On 10th April, the police in Amritsar fired upon a peaceful procession provoking widespread attacks on banks, post offices and railway stations. Martial law was imposed and General Dyer took command. 
6)  After the brutal killing and massacre of Jallianwala Bagh, violence spread nationwide and as a result, Mahatma Gandhi called off this Rowalatt Satyagraha movement