The correct answer to this open question is the following.
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Jus ad bellum is the kind of legislation that authorizes the transition from a state of peace and agreement to a state of war, where the use of the armed forces is justified. It implies that just a legitimate authority can wage war when no other option is left. Just ad bellum have some principles, that include: right authority, right intention, proportionality, reasonable hope, and last intention, which can be understood as the case in which war is the last resource after a long period of diplomacy and negotiation, under the right authority and the valid reasons to proceed as the last resource to solve an issue.