This Article is focused on efforts to accommodate, within the confines of international humanitarian law, militant responses to acts of cross-border terror violence, as exemplified in most recent times by atrocities committed by the Islamic State of Iraq and Levant (ISIL) and its successor, the Islamic State in Iraq and Syria (ISIS). Since World War I (1914-1918), the international community of States sought to commit itself to settle international disputes by peaceful means and not through the power of the sword. The Charter of the United Nations (U.N. Charter) seemingly confined legitimate armed interventions to those authorized by the Security Council to bring to an end situations that constitute a threat to the peace, a breach of the peace, or an act of aggression (Article 42), and instances of self-defense where a Member State has been attacked (Article 51). However, over time jus ad bellum has extended legitimate armed interventions well beyond the confines of the U.N. Charter to also include armed interventions authorized by the General Assembly in very special circumstances--wars of liberation, pre-emptive self-defense action, and humanitarian intervention. It has also come to be accepted that a government confronted by insurgents can invite other States to come to its assistance. Iraq has indeed done so, and therefore the airstrikes against ISIS strongholds by, for example, American forces in Iraq, are lawful under the norms and customs of contemporary international humanitarian law. However, the United States has also launched airstrikes against al-Qaeda and ISIS targets in Syria while not having been requested by the Syrian government to do so. In order to afford legality to those airstrikes, members of the Obama Administration have proposed a new rule of humanitarian law, the "unwilling or unable rationale," proclaiming that armed forces of State A can take military action against terrorist groups located in State B if the government of State B is either unwilling or unable to prevent its territory from being a launching pad for acts of terror violence. Although some proponents of the unwilling or unable rationale attempted to bring the legality of such military action within the confines of self-defense action or humanitarian intervention, this Article argues that the unwilling or unable rationale does not fit the standard conditions of legitimate self-defense or the essential objectives of humanitarian intervention. The Article concludes that the unwilling or unable rationale is a new norm of jus ad bellum in the making. A side issue of the Article addresses the question of why spokespersons of the Obama Administration persist in referring to ISIL in spite of the fact that the organization in June 2014 changed its name to ISIS. It is noted that al-Qaeda was part of ISIL but is not part of ISIS, that the Obama Administration did not receive congressional approval for the airstrikes in the Middle East, and that the Obama Administration relies on congressional approval of the post 9/11 war against terror that was focused on the Taliban and al-Qaeda forces in Afghanistan and the 2003 invasion of Iraq to afford constitutional legality to the airstrikes in Iraq and Syria. Since al-Qaeda was part of ISIL but not of ISIS, referring to ISIL is most likely intended to bring these airstrikes within the reach of the congressional approvals of yesteryear. [ABSTRACT FROM AUTHOR]