On Vaisakhi 1978 a convention of the Sant Nirankari Mission was held at Amritsar. A group of Sikhs, from the Akhand Kirtani Jatha and the Damdami Taksal, marched from the Golden Temple to protest against it.
There was a confrontation and firing. Thirteen Sikhs were killed. The subsequent trial at Karnal acquitted the accused, which was received in Punjab as a failure of the state to protect Sikhs and became a central grievance.
The date is generally taken as the beginning of the sequence that ran through the following decade.
The two sides' accounts of what happened that day are entirely different and have never been reconciled.
This page states the sequence and the outcome of the trial. It does not attribute responsibility, because no process has.
The Nirankari convention was held at Amritsar on the day of the Vaisakhi gathering, which is the fact that made a confrontation likely. A group left the diwan at Manji Sahib to protest at the convention and the firing occurred after it arrived.
The trial was moved out of Punjab to Karnal in Haryana and ended in 1980 with the acquittal of all the accused on the ground of self defence. The acquittal, more than the killings, is the point from which the following decade is usually traced.
The head of the Nirankari mission was killed in Delhi in 1980. The sequence from there runs through the arrests, the confrontation at the Darbar Sahib complex, and Operation Blue Star, and every account of it is contested in its details.