God placed some limitations on the authority of a king. He's not allowed to...

-Rely on military strength or alliances for security. There's nothing wrong with a strong military or being friendly with neighboring nations, but God is our true defense.
-Use his office for personal enriching himself at the expense of the people, whether in gold, women, property, or anything else. There's nothing wrong with wealth or even in using your position to earn it. The problem is in abusing your position. No bribes, unjust taxes, property confiscations, or other perversions of justice.

All leaders need to remember that they exist for the sake of their people and their mission, never the other way around.