How does just war theory distinguish between deciding to go to war and conduct during war?

Just war theory distinguishes between the decision to enter a conflict and the behavior of forces during that conflict by utilizing two distinct Latin frameworks: jus ad bellum and jus in bello.12

Jus ad Bellum: The Right to War

Jus ad bellum concerns the justification for resorting to armed force. To be considered just, a war must meet specific criteria, including:
* Proper Authority: The war must be declared by a legitimate sovereign authority.1
* Just Cause: It must be a response to grave injustice or a defense of the common good.1
* Right Intention: The war must be waged for justice rather than self-interest.1
* Last Resort: Peaceful alternatives must be exhausted.12
* Proportionality and Success: The expected benefits must outweigh the costs, and there must be a reasonable chance of success.12

Jus in Bello: Conduct in War

Jus in bello governs the conduct of forces once a war has begun, focusing on limiting the means and methods of conflict. Key principles include:1
* Discrimination: Targets must be limited to combatants and legitimate military or industrial complexes.1
* Proportionality: The force used must be proportionate to the objective.1
* Prohibited Methods: Combatants must avoid unjust acts, such as torture or genocide.1

These standards are reinforced by international law, notably through the Geneva Conventions.12