What is one power the federal government has that relates to military?

The federal government has the exclusive power to create an army as part of its responsibility for national defense and security. This authority is outlined in the U.S. Constitution, specifically in Article I, Section 8, where it states that Congress has the power "to raise and support Armies." This responsibility includes the recruitment, training, and organization of military forces to protect the country from external threats and to conduct military operations as needed.

The other options relate to different levels of government and their respective responsibilities. While maintaining state guards pertains to the authority of individual states, controlling local police forces is a function of local and state governments. Appointing military leaders can involve both federal and state levels but is primarily handled through federal mechanisms such as the President's role as Commander in Chief of the Armed Forces. Thus, the ability to create an army is a distinctly federal power, central to its role in ensuring national security.