International humanitarian law violations, legal responsibility, and US military support to the Saudi coalition in Yemen: a cautionary tale

ABSTRACT This article considers international humanitarian law violations and legal responsibility in relation to US military support provided to the Saudi Arabia-led coalition fighting a non-international armed conflict in Yemen. Through this example, this article examines the broader issue of states not party to an armed conflict providing military assistance to states that are party to a conflict in a manner that may blur legal responsibility and undermine accountability. To do so, it considers this military assistance in relation to the use of force, state responsibility, and international humanitarian law. First describing the US military assistance provided to the Saudi coalition, the article then assesses the lawfulness of the coalition’s use of force, whether the United States became a party to conflict, if the United States violated the law of state responsibility, and finally whether the United States adhered to its Common Article 1 duty to respect and to ensure respect.