Alma 49:6 - 49:10
Alma 49: 6 Now the leaders of the Lamanites had supposed, because of the greatness of their numbers, yea, they supposed that they should be privileged to come upon them as they had hitherto done; yea, and they had also prepared themselves with shields, and with breastplates; and they had also prepared themselves with garments of skins, yea, very thick garments to cover their nakedness.
The commanders of the Lamanite army, considering their vast number of men, thought they could just attack anywhere and would prevail. In times past, their fighters were not protected with any kind of body armor, but this time, taking a lesson from previous battles with the Nephites, they were now cover in protective clothing.
Alma 49: 7 And being thus prepared they supposed that they should easily overpower and subject their brethren to the yoke of bondage, or slay and massacre them according to their pleasure.
So the Lamanites thought with their superior numbers and their armor they could take any of the Nephite armies or towns and make them either slaves or destroy them at their will.
Alma 49: 8 But behold, to their uttermost astonishment, they were prepared for them, in a manner which never had been known among the children of Lehi. Now they were prepared for the Lamanites, to battle after the manner of the instructions of Moroni.
However, in this, the Lamanites were frustrated. Moroni had now use a totally different tactic against the Lamanites. In fact his approached was completely different from any defensive posture that had ever been used in the past.
Alma 49: 9 And it came to pass that the Lamanites, or the Amalickiahites, were exceedingly astonished at their manner of preparation for war.
The Lamanite commanders were perplexed as to how to counteract against the new defensive concepts put in place by Moroni.
Alma 49: 10 Now, if king Amalickiah had come down out of the land of Nephi, at the head of his army, perhaps he would have caused the Lamanites to have attacked the Nephites at the city of Ammonihah; for behold, he did care not for the blood of his people.
Amalickiah was not with this invading Lamanite army. If he was there, he would have just commanded the army to attach the Nephites fortifications regardless of the possible causalities. Since Amalickiah could care less about his people, they would have been commanded to attack.