The main consequence of the Peterloo Massacre in England, which occurred on August 16, 1819, was a significant shift in public opinion regarding the need for political reform. The massacre, which involved the cavalry charging into a peaceful rally demanding parliamentary reform, led to outrage and increased awareness of the plight of the working class. It galvanized the movement for reform, ultimately contributing to the passage of the Reform Act of 1832, which expanded voting rights to middle-class men. The event highlighted the disparities in political power and social justice, prompting discussions about democracy and citizenship in Britain.