What established the Marine Corps composition and function?

Title 10 of the United States Code is the legal foundation that establishes the structure, composition, and function of the United States Armed Forces, including the Marine Corps. It outlines the roles and responsibilities of military branches, detailing their organization, command structure, and operational authority.

For the Marine Corps, Title 10 provides the statutory basis that guides how the Corps operates within the larger framework of U.S. military policy. It specifies the mission, authority, and the organizational setup of the Marine Corps, making it essential for understanding its operational parameters and integration with other military services.

The other options, while they play various roles in military governance, do not specifically codify the Marine Corps' composition and function in the same manner. Military regulations and executive orders provide guidelines and directives but are not comprehensive in laying the foundational legal structure that Title 10 offers. International treaties may govern certain interactions and conduct but do not dictate the internal organization and functions of the Marine Corps itself.