Which of the following is a key component of military law?

The Uniform Code of Military Justice (UCMJ) is a foundational component of military law, serving as the primary body of laws that govern the conduct of members of the armed forces. It establishes legal standards and procedures for military personnel, covering a wide range of offenses, including desertion, insubordination, and conduct detrimental to the service. The UCMJ ensures that military members are held accountable under a legal framework tailored to the unique needs of military discipline and readiness, enabling commanders to enforce order and maintain good order and discipline within the ranks.

The other options, while significant in their own contexts, do not serve as core components of military law in the same way. The Posse Comitatus Act pertains to the limits on the use of federal military personnel in domestic law enforcement, the War Powers Resolution governs the executive branch's authority to engage in military actions abroad, and Army Regulation 600-20 deals specifically with army command policy, including areas like equal opportunity and sexual harassment. These elements support the broader context of military operations and governance but do not constitute the legal framework that directly regulates military behavior as the UCMJ does.