The riots were a result of rising [Protestant Religious Fundamentalist] anti-Catholic sentiment at the growing population of Irish Catholic immigrants.
In the five months prior to the riots, [Protestant Religious Fundamentalist] groups had been spreading a rumor that Catholics were trying to remove the [King James] Bible from public schools. A [Protestant Religious Fundamentalist] rally in Kensington erupted in violence on May 6 and started a deadly riot that would result in the destruction of two Catholic churches and numerous other buildings.
Riots erupted again in July, after it was discovered that St. Philip Neri's Catholic Church in Southwark had armed itself for protection. Fierce fighting broke out between the [Protestant Religious Fundamentalist] and the soldiers sent to protect the church, resulting in numerous deaths and injuries...
During the 1840s, students in Philadelphia schools began the day with reading the Protestant version of the Bible. On November 10, 1842, Philadelphia's Roman Catholic Bishop, Francis Kenrick, wrote a letter to the Board of Controllers of public schools, asking that Catholic children be allowed to read the Douai version of the Bible, used by Roman Catholics. He also asked that they be excused from other religious teaching while at school. As a result, the Board of Controllers ordered that no child should be forced to participate in religious activities and stated that children were allowed whichever version of the Bible their parents wished.
Approximately one year later, a rumor was circulated that Hugh Clark, a Kensington school director who was Catholic, was visiting a girls school, where he demanded that the principal stop Bible reading in school. The story also claimed that the principal refused and that she would rather lose her job. Hugh Clark denied this version of events and claimed that after finding out several students had left a Bible reading to read a different version of the Bible, he commented that if reading the Bible caused this kind of confusion, that it would be better if it was not read. [Protestant Religious Fundamentalist] Anti-Catholics used the story to spur anti-Catholic sentiments by claiming that Catholics, with direct influence from the Pope, were trying to remove the Bible from schools. [Protestant Religious Fundamentalist] Anti-Catholic groups further inflamed hostile feelings towards Catholics by twisting Bishop Kenrick's requests to the Board of Controllers into an attack against the Bible.
[Protestant Religious Fundamentalists] groups denounced the Catholics and called on Americans to defend themselves from "the bloody hand of the Pope."
During the early riots, at least fourteen were killed, an estimated fifty people were injured, two hundred fled their homes, and damage totaled an equivalent to $3.8 million in present-day terms.
...After the riots, Bishop Kenrick ended his efforts to influence the public education system and began encouraging the creation of Catholic schools, with 17 being founded by 1860."