Alma 46:29

And it came to pass that when Amalickiah saw that the people of Moroni were more numerous than the Amalickiahites; and he also saw that his people were doubtful concerning the justice of the cause in which they had undertaken; therefore, fearing that he should not gain the point, he took those of his people which would, and departed into the land of Nephi.

Amalickiah saw that the people of Moroni were more than the Amalickiahites. He also saw that his people were not sure if their fight was right. He was afraid he would not win. So he took the people who would follow him and left to the land of Nephi.

When Amalickiah saw that Moroni’s supporters far outnumbered his own people, and saw that his followers were starting to doubt whether their cause was even right, he got scared. Afraid he’d lose, he took whoever would follow him and fled to Lamanite territory.