The Jallianwala Bagh Massacre happened a long time ago in India, in the year 1919. This was when India was ruled by British people. There was a big park called Jallianwala Bagh in Amritsar city in Punjab, India. Lots of people came to this park to celebrate a festival called Baisakhi.
But some British soldiers, led by a man named General Dyer, came into the park and started shooting at the people who were peacefully gathering there. The soldiers didn't give any warning or tell the people to leave the park. They just started shooting at them with rifles.
Many people got hurt and some even died. This was a very bad thing to happen because it was unfair and cruel. The people who got hurt or lost their family members were very sad and angry.
After this, many Indians protested against the British rule and wanted to be free. This eventually led to India gaining independence from British rule in 1947.