On August 6th 1855, members of the anti-immigrant American Party (more commonly referred to as the Know Nothings) attacked Catholic Irish and German Immigrants. Prior to the violence, armed Know Nothings stood at polling stations to prevent the Catholics from voting in the mayoral election. To increase the intimidation, the Know Nothings began to vandalize and burn Irish property as well as stoned a priest. In the violence, at least 22 men and women were killed and many more were injured. In one infamous episode, a man was actually pushed back into a burning building. St. Martins Church and the Cathedral of the Assumption were nearly destroyed by the mob, only stopped by the mayor while other buildings burned. While five men were arrested for the violence no one was convicted and there was no compensation for the victims.
The riots would make the beginning of the end for the Know Nothings as the party's behavior had alienated some of their support and soon nativist sentiments would be completely overshadowed by the looming issue of slavery.