The Peterloo Massacre took place at St Peter's Field, Manchester, Lancashire, England, on Monday 16 August 1819. Fifteen people died when cavalry charged into a crowd of around 60,000 people who had gathered to demand the reform of parliamentary representation.

After the end of the Napoleonic Wars in 1815 there was an acute economic slump, accompanied by chronic unemployment and harvest failure due to the Year Without a Summer, and worsened by the Corn Laws, which kept the price of bread high. At that time only around 11 percent of adult males had the vote, very few of them in the industrial north of England, which was worst hit. Reformers identified parliamentary reform as the solution and a mass campaign to petition parliament for manhood suffrage gained three-quarters of a million signatures in 1817 but was flatly rejected by the House of Commons. When a second slump occurred in early 1819, radical reformers sought to mobilise huge crowds to force the government to back down. The movement was particularly strong in the north-west, where the Manchester Patriotic Union organised a mass rally in August 1819, addressed by well-known radical orator Henry Hunt.