Final answer:
Forces engage unprivileged belligerents when it is legally justified and necessary to protect state interests, in situations assessed for favorable outcomes with minimal sacrifice, and within the bounds of international humanitarian law, especially as codified by the Geneva Conventions.
Step-by-step explanation:
Forces are allowed to engage unprivileged belligerents during a conflict when certain conditions are met under international law and the rules of engagement. These conditions often relate to the ability and the necessity to defend and protect state interests, prevent greater harm, or retaliate against unlawful actions. The Geneva Conventions and other international humanitarian laws dictate the treatment of combatants and non-combatants, providing clear definitions and protections to prevent war crimes. However, in modern conflicts, such as the war on terror, new categories such as 'unlawful combatants' have emerged, leading to contentious debates over lawful engagement and the treatment of prisoners.
Engagement is deemed necessary when a state needs to protect its citizens or assert its political goals when faced with a strong possibility of successful outcomes against weaker or distracted states. However, the favorability of engaging unprivileged belligerents is not solely based on the potential for success; it also has to consider the minimization of sacrifices and the adherence to international legal standards. Presidential authorizations, UN resolutions, NATO actions, and other forms of legitimate international support may influence the decision to engage in combat.
Despite the existence of lawful frameworks governing warfare, some states may opt to ignore these rules to achieve their objectives, prompting the need to resort to force. This introduces significant challenges regarding the balance between national security and human rights. Supreme Court rulings, like Hamdan v. Rumsfeld, highlight the ongoing struggle between wartime necessities and legal obligations, where constitutional laws and the Geneva Conventions have had to be interpreted within the context of modern warfare.