The National Guard occupies an unusual position in American government, belonging to a state and to the nation at once. Which of those relationships is active at any moment is a legal question.
The dual structure is the starting point
Guard units are organized within individual states and territories, and in ordinary times they report through a state chain of command headed by the governor.
The same units are also part of the reserve component of the national armed forces, equipped and trained to federal standards so they can be absorbed into a larger force.
That dual identity is deliberate. It preserves a force the states can direct while keeping it interchangeable with the regular military when the country needs it.
State activation is the common case
Most call-ups are ordered by a governor and remain under state authority, typically for storms, floods, wildfires and other events where the state needs organized manpower quickly.
In this status the state directs the mission and generally bears the cost, and members operate under state law rather than under the rules that govern federal forces.
Because the units live in the communities they serve, they can often reach an affected area faster than help arriving from outside the state.
Federal service changes the chain of command
When units are ordered into federal service, they leave state control entirely and report through the national military chain, with the federal government paying and directing them.
Mobilized units in this status are treated as part of the regular force, which is how Guard members come to serve on overseas deployments alongside active-duty units.
The distinction matters because the legal constraints on what military personnel may do domestically differ depending on which status they are serving under.
A middle status exists between the two
A third arrangement keeps units under the governor's command while the federal government funds the activity, and it is used for training and for certain agreed domestic missions.
This hybrid exists because many missions have both state and national dimensions, and it lets the two levels of government share a task without either surrendering its role.
Which status a given activation falls under is set out in the order authorizing it, and the specifics are governed by statute that changes over time.
Members carry civilian lives alongside
Most Guard members serve part time, training on a recurring schedule while holding ordinary civilian jobs, which is what makes the force comparatively inexpensive to maintain.
Federal law provides employment protections for members called away, covering matters such as reinstatement after service, though the details are intricate and depend on circumstances.
Extended or repeated activations put strain on that arrangement, since employers and families absorb an absence whose length is often not known when it begins.