""The Apostolic Letter of Pope Pius IX: To All Protestants and Other Non-Catholics"" is a historical document written by Pope Pius IX in 1870. In this letter, the Pope addresses all Protestants and non-Catholics, urging them to reconsider their beliefs and convert to Catholicism. He argues that the Catholic Church is the only true church established by Jesus Christ, and that all other religions are flawed and incomplete. The letter also addresses...