The functionalist theory, a macro view of how the parts of society serve to maintain stability, can be used to explain and understand the health care system and all of its many interrelated parts. This system is comprised of social structures and social institutions. For example, the U.S. health care system is based on the social structure of free market capitalism rather than models employed in other countries where the government both provides and pays for health care (i.e. United Kingdom, Italy, New Zealand, and Spain). This is important to note, as there is ongoing debate about how to change and improve the U.S. health care system. By changing one facet of the system it potentially changes and disrupts other components. For example, the Affordable Care Act (ACA), also known as Obamacare, created a new structure for Americans to receive health care from exchanges, or marketplaces that help individuals, families, and small businesses shop for and enroll in affordable medical insurance.  The ACA mandated that all individuals have health insurance by law. After three years, many of the large insurers such as Aetna, UnitedHealth, and Humana have decided the exchanges are not profitable and are withdrawing from the marketplace. This is leaving some Americans with only one or no health insurance options to choose from. This reduces the options for insurance coverage even further for those who have historically been too sick or too poor to access coverage. This decision by health insurance corporations creates dysfunction and is exact opposite of the intent of Obamacare. Changing one aspect of the health care system negatively impacted insurance companies and potentially threatens the stability of the entire health care system.