What is the amritsar massacre remembered for?

Amritsar is an important place for Sikhs as The Harmandir Sahib (Golden Temple) is located there. The Golden Temple is the Supreme court for Sikhs and all community conflicts are solved there. Harmandir Sahib (Golden Temple) is also known as the Akal Takht. The Akal Takht is the highest seat for the Guru Granth Sahib.

the guru granth sahib is a book which has a collection of hymns or shabad, which describe what God is like and the right way to live. Just like how Muslims have the quran, or how the christians have The Bible.