How did the United States healthcare system develop? e.g. health insurance, Medicare.?

-Why does the United States have health insurance? It is optional to have health insurance, because it is not required by any law, unlike auto insurance. I would like to know where the system of health insurance got it's roots.Traditionally health insurance has been offered by employers and was included in your employment for free. In the last 20 years or more, the employee has had to pay part of the premiums which have increased. It is cheaper than buying your own insurance because your employer gets a group discount. Until the 1960s most people did not have health insurance and paid cash for care but part of the civil rights and Great Society of the 60s was to ensure seniors not suffer for lack of money to pay for medical care. In 1965 Title XVIII of the Social Security Act came into being as Medicare. Since then millions of others are enrolled in Medicare beside seniors. The premiums have increased over the years.