Alma 59:8

And their armies were so numerous, that the remainder of the people of Nephihah were obliged to flee before them; and they came even and joined the army of Moroni.—

Their armies were so big that the rest of the people of Nephihah had to run away. They joined Moroni’s army.

Their armies were so massive that the survivors had no choice but to flee. They retreated and joined Moroni’s army.