The Mission of Alma the Younger
The city of Ammonihah is first mentioned in Alma 6:6 circa 82 B.C. when Alma the Younger, after having preached in the city of Melek, comes upon the city after traveling northwards for three days. After initially being rejected by the people, Alma leaves the city, but is met by an angel, which instructs him that he is to go back on an especial mission to declare that if the city does not repent, then it would be destroyed. The great urgency of this mission was due to the fact that the people of the city of Ammonihah were plotting to destroy the freedoms of the Nephite people.
Upon returning, Alma meets up with Amulek who becomes a companion in Alma's mission and a second witness to the truths that he declares.
The city of Ammonihah is known for the wickedness of its lawyers and it is with these characters that Alma and Amulek have their initial confrontation. The most notable of these was Zeezrom who initial tries to entrap them, but is finally convinced by the testimony of Amulek and brought to repentance.
The people at large, however, are unrepentant. Many righteous people flee the city, or are cast out, while Alma and Amulek are cast into prison. The righteous people who remain are burned while Alma and Amulek are forced to look on. Finally, after enduring more persecution while in prison, Alma and Amulek are freed by the power of the Lord which causes the ground to shake and the prison to tumble to the ground.
The end result is that the people did not repent and, having cast out or killed all of the righteous, the city is prepared for the promised destruction.
In Alma 16:2-3,9-11 the destruction of the city of Ammonihah is described, occurring at about 80 B.C. The destruction of the city of Ammonihah is brought about by the Lamanites, who in a fit of genocidal rage, swiftly fall upon the city and destroy it, killing every inhabitant within one day. The anger of the Lamanites which brought about the attack was in consequence of the Christian religion's being adopted by a large group of Lamanites (who came to be known as the Anti-Nephi-Lehis), which religion was, up until that time, almost exclusively a Nephite religion.