Alma 49:11 - 49:15
Alma 49: 11 But behold, Amalickiah did not come down himself to battle. And behold, his chief captains durst not attack the Nephites at the city of Ammonihah, for Moroni had altered the management of affairs among the Nephites, insomuch that the Lamanites were disappointed in their places of retreat and they could not come upon them.
Since Amalickiah had not come down with his Lamanite army to keep his commanders motivated, they decided that attacking Ammonihah was not a good move at the moment. Moroni had changed the management of the leaders of these areas so that he had total say in what the Nephite defense posture would be. The Lamanites thinking that they could use Ammonihah as a place of retreat in case the future battles did not go their way, had no choice but to return back into the wilderness.
Alma 49: 12 Therefore they retreated into the wilderness, and took their camp and marched towards the land of Noah, supposing that to be the next best place for them to come against the Nephites.
They then started out for the land of Noah. They thought it would not be defended as was Ammonihah and should be easy to take.
Alma 49: 13 For they knew not that Moroni had fortified, or had built forts of security, for every city in all the land round about; therefore, they marched forward to the land of Noah with a firm determination; yea, their chief captains came forward and took an oath that they would destroy the people of that city.
As the Lamanites marched towards Noah, they were completely unaware of the efforts by the Nephites under the leadership of Moroni to fortify and strengthen the Nephites cities near the wilderness. The frustration of finding Ammonihah well defended, angered the Lamanite leaders and they swore an oath to conquer and destroy those they would find in the land of Noah.
Alma 49: 14 But behold, to their astonishment, the city of Noah, which had hitherto been a weak place, had now, by the means of Moroni, become strong, yea, even to exceed the strength of the city Ammonihah.
However, when the Lamanites entered the land of Noah, they found it even more fortified than was Ammonihah.
Alma 49: 15 And now, behold, this was wisdom in Moroni; for he had supposed that they would be frightened at the city Ammonihah; and as the city of Noah had hitherto been the weakest part of the land, therefore they would march thither to battle; and thus it was according to his desires.
Moroni knew in his mind what the Lamanites would do when they saw Ammonihah. He figured that if they saw the fortifications at Ammonihah, they would not attack it and would instead march to Noah because in the past it had been weakly defended. It was at Noah that Moroni concentrated his forces because he knew the Lamanites would probably not pass it up and attack it anyway.