Okay kiddo, let me explain about the Philadelphia Nativist Riots like you are 5 years old.
There was a time many years ago in Philadelphia when people from different countries were coming to live there. Some of the new people were Catholics who followed a different religion than the Protestants who already lived there.
Some of the people who were already living there were worried that the new people would change their city, jobs, and home. So, they started to get angry and protest. They called themselves "nativists," which means they thought they were the real Americans and the new people were not.
The protests turned into a riot, which means many people were fighting with each other, and it became violent. People were breaking windows, setting buildings on fire, attacking each other, and even killing others.
The mayor of Philadelphia tried to stop the violence, but he wasn't very successful. The violence went on for three whole days! People were really hurt, and some even died.
In the end, the riots stopped, and people tried to fix the damage. The leaders of the city realized they needed to do better at making sure everyone was treated fairly, no matter where they came from or what their religion was.
So, that's what happened during the Philadelphia Nativist Riots. It was a very sad time when people didn't get along and hurt each other because they were afraid of change. But hopefully, we can learn from this and make sure we treat each other with kindness and fairness.