Which power allows the federal government to create an army?

The power that allows the federal government to create an army is classified as delegated powers. Delegated powers are those specifically granted to the federal government by the Constitution. The authority to raise and support armies is enumerated in Article I, Section 8 of the U.S. Constitution, where Congress is given the power to provide for the common defense and to raise and support armies. This reflects the intention of the framers of the Constitution to create a strong central government capable of addressing national defense concerns.

The other categories of powers do not pertain to the creation of an army. Reserved powers are those powers not delegated to the federal government and are reserved for the states, while concurrent powers can be exercised simultaneously by both state and federal governments. Implied powers are those not explicitly stated in the Constitution but are necessary to implement the delegated powers. While implied powers can also support military actions, the specific authority to create an army falls clearly under the realm of delegated powers.