故上兵伐謀, 其次伐交, 其次伐兵, 下政攻城
Destroy the enemy’s plan is the best.
During the war, we need a full preparation to besiege a walled city. It will spend a lot of time.
The general may lose their patience before the engines of attacking prepared.
Therefore, the skilled generals will overthrow their kingdom without any operations. They will not harm individuals but destroy the government. The typical instance is the Wu Wang, who put an end of the Yin dynasty.
This means divide our armies, not enemy’s.
Though a small troop can wage a wall, it will be captured by a large troop probably.
不知三軍之事, 而同三軍之政者, 則軍士惑矣;
Opportunism and flexibility are different than the strategy of governing a state. Morality and li is only fitful for governing a state.
So many military disasters were caused by undue interference from distant government.