Just war is divided into three parts; jus ad bellum, (the justice of choosing war), jus in bello (justice of actions in war) and jus post bellum (justice of peace accord and the end of the period of war).
The rules of jus ad bellum are relevant to the heads of states. This is for the reason that they are the ones who start wars. To justify any choice going into war, several conditions must be met. The country must; start war for justified reasons (self-defense or defense of others i.e. wrongs received), and intend to fight the war for its justified reason (not an ulterior motive). The decision to go to war must be made by the correct authority according to the law and made public i.e. to its own citizen and the enemy state. The country must exhaust all possible peaceful options before resorting to war. A country must be sure it has high chances of success to avoid futile mass violence. It must ensure that the universal good expected outweighs possible evils.
Justice in war addresses the conduct of military in combat and concerns military commanders. Justice in war tackles the rule to be adhered to regarding the enemy and its armies and the aggressor country's people as it fights. The aggressor should obey international laws on weapons that can be used, target only armed soldiers and observe non-combatant immunity. The aggressor can only used force that is proportional to the ends it seeks, provide prisoners of war with humane quarantine and exchange them for one owns prisoners of war. The aggressor should not use "evil weapons". Countries should also not retaliate when the enemy violates just in bello.
Jus post bellum regulates the termination of war. The peace settlement between the involved parties ought to be reasonable and public. It should secure the triggers of the conflict. It also should make a difference leaders, soldiers and civilians. In cases where the defeated country has committed blatant violation of rights, punishment must be meted and the same goes for soldiers who committed war crimes. Compensations after the war must also be proportional and non-discriminatory and finally the aggressor must provide an opportunity for the defeated country to carry out reforms.