Alma comes to the city of Ammonihah and finds that “Satan had gotten great hold upon the hearts of the people of the city of Ammonihah.” What did he find? The particulars of the confrontation in Ammonihah will center around the mission of the Atoning Messiah, so the certain “problem” in Ammonihah is that they do not believe in this aspect of Nephite religion. It is interesting that Ammonihah does consider itself connected to the political authority of Zarahemla, but disassociated with the religion of Zarahemla, or at least this particular aspect of it. It is not until Alma 14:16 that we learn that the order of Nehor is present (and probably prevalent) in Ammonihah. The best answer to the “hold of Satan” is that Ammonihah has followed the order of Nehor, with all of the ideological trappings that flow from that apostate religion.
We have seen the order of Nehor as an important alternative religious systems in the beginning of Alma, and it was analyzed as the presence of outside influences on the Nephite ideology. It is logical that Ammonihah would be particularly susceptible to these outside influences if for no other reason than their distance from Zarahemla, which clearly makes it easier to have a different set of beliefs from Zarahemla.