The individual subsystems that make up the larger U$.$ S$.$ health care system are:

The "subsystem" that serves those people and their dependents who are regularly employed and have health insurance available to them from their employer

The $"$ subsystem" that serves military veterans who are eligible to use the Veterans Administration hospitals

The "subsystem" that covers injuries and illnesses related to the workplace, generally known as the worker's compensation system

The "subsystem" that serves those people who are not regularly employed or who are impoverished to some degree, and who do not receive sustained health insurance coverage from an employer

All of the above