“Until the major provisions of the ACA went into effect in January 2014, health insurance coverage was always voluntary. About 30% of the population was covered through the two major public programs enacted in 1965: Medicare for seniors (later extended to the disabled) and Medicaid for poorer Americans . Most others received coverage through their employment, either as employees or dependents, but such coverage was always voluntary: employers did not have to provide it, and individuals were not required to buy it. Less than 10% purchased coverage on their own.
“As far back as the 1950s those with pre-existing illnesses generally found individual insurance policies unaffordable because insurers could charge higher premiums to those with a history of illness. The ACA increased individual coverage by: prohibiting insurance companies from excluding people or charging more for pre-existing conditions; mandating that all individuals obtain insurance; and by helping individuals pay for this through income-based premium subsidies.”
Source: Thomas Rice, Lynn Y. Unruh, Ewout van Ginneken, Pauline Rosenau, Andrew J. Barnes, Universal coverage reforms in the USA: From Obamacare through Trump, Health Policy, Volume 122, Issue 7, 2018, Pages 698-702, ISSN 0168-8510, https://doi.org/10.1016/j.healthpol.2018.05.007. http://www.sciencedirect.com/science/article/pii/S0168851018301544