The key to understanding verse 2 is verse 3. There were the beginnings of a division among the people. Mormon does not tell us why the contentions arose, but the fact that there was less than unanimous support for King Noah explains why the forces of the king had been reduced. In many ancient societies, the military was made up of the people who were otherwise the farmers and laborers. There was no standing army. Thus, there were no paid positions, and the reduction of the forces likely signifies that when many of the people began to dissent from King Noah’s reign, they also would not have answered the call to a military operation.
The reason for mentioning the reduction in the numbers in the forces of the king has little to do with the story, except that it provides the essential background of a people divided and ready for change. That is the backdrop for the story of Gideon, which begins in the next verse.