War, by default, is a chaotic mess where no one can truly win without suffering a few losses in the process.
However, there are some factors one can control to keep that number as low as possible.
First, one could make sure that their army is of sufficient size and quality.
The larger the army, the more likely the soldiers will be able to protect each other from attacks. Of course, said soldiers need to be taught to do so.
Second, the weapons wielded.
An army using weapons that outclass their opponents is more than likely going to take them out before they could cause any real damage to them.
Third, the terrain on which the war is waged.
Defending a narrow passage turns a large army into a liability and makes a small army thrice as deadly, while an open field has the opposite effect.
An army stationed on top of a steep hill can easily defend against attackers, while those on the bottom of a hill can set up a barricade and trap their opponents with ease.
