The correct answer to this open question is the following.
The principle of the Just War Theory that is best supported by the declaration of war is the following: "A just war can only be waged only as a last resort. All non-violent issues must be exhausted before the use of force can be justified."
That is why countries have signed the declarations of Geneva or Hague, to agree to initiate or participate in a war just, and only just in the case that no other option is left. Experts, historians, social leaders, Non-governmental groups, and religious leaders agreed that war is the wors option and never be waged again, that is why the governments must contemplate other options to solve problems.
