What are the key differences from how the US healthcare system utilizes preventitive services and what have been the key drivers in the shift towards prevention?

I am trying to understand how/why the healthcare system has shifted more towards preventitive services in the past 25 years. Particuarly, how have cost of services rising, insurance, governemnt regulation, the aging population and chronic disease influences this? I am trying to fit this idea into an essay i am working on and dont understand what took place to change our orientation to prevention during these 25 years. (I do understand during 1900-2000) thanks!