If Army size accounts for so much of net value, why will nations attack?
You will have to determine how strong your nation will be compared to another player who does attack at the end of the month. If you attack another player and win you will lose some armies but you will gain territory, money and buildings from that attack. The amount you gain from an attack is worth much more in the long run then not attacking. Remember Zhanshen is a war game–this is why armies are very important in the score and value of your nation. The important items for your nations score are: armies, knowledge and territory.