"Commanders, staffs, and subordinates must ensure that their decisions and actions comply with applicable US, international, and in some cases host-nation laws and regulations." --Preface
In August 2019, The Commander's Handbook on the Law of Land Warfare--Field Manual FM 6-27/MCTP, was released by the US Army and the US Marine Corps. It "provides a general description of the law of land warfare for Soldiers and Marines, delineated as statements of doctrine and practice, to guide the land forces in conducting disciplined military operations in accordance with the rule of law." Although this publication is designed to be a useful tool for its intended audience, Army and Marine Corps commanders as well as Army and Marine Corps judge advocates, The United States Department of Defense Law of War Manual (also available from Cosimo Reports) remains the authoritative statement on the law of war for the US Department of Defense.
Some other related publications by Cosimo Reports are: Instructions for the Government of Armies of the United States in the Field--The Lieber Code (1863), The Law and Usages of War at Sea--A Naval War Code (1900), Small Wars Manual (1940) Rules of Land Warfare (1940), and others.
The US ARMY is one of three military departments in the United States (Army, Navy, and Air Force) which reports to the Department of Defense. It is comprised of two distinct and equally important components, active and reserve. The reserve components are the US Army Reserve and the Army National Guard.
The US MARINE CORPS is a branch of the US Armed Forces responsible for conducting expeditionary and amphibious operations with the US Navy, as well as the Army and Air Force.