It took place at a peaceful protest of tens of thousands of people who wanted parliamentary reform, at a time when only 2% of people had the vote. The protest was charged by the local cavalry and tens of people were killed and hundreds injured.
A reform act was passed in 1832, after more protests, riots and conflict. Campaigns for reform and representation carried on with the Chartists in the 19th century and women’s suffrage in the 20th.
Gotta fight for what you want.