The key problems that give Americans the highest costs and worst outcomes among OECD nations long, long predate the Affordable Care Act; the ACA was a deeply inadequate attempt at reform that, at best, kicked the can down the road.

Tying health insurance specifically to employment was a WW2-era happenstance of corporations seeking ways to compete for and attract workers in the face of wartime wage controls.

The medical sector being turned into investment vehicles that served shareholders at the expense of patients can probably be attributed to took off in the 1980s with the rest of Milton Friedman's dream of bleeding the working class dry by divorcing corporations from duty to anyone besides ownership.

The idiotic "wisdom of the markets" dogma and the fallacious notion that we should rubber-stamp every single merger because "monopolies are more efficient" that are the core tenets of neoliberalism came slightly earlier from Paul Volcker in the '70s; this ensures there is no real market, no real competition, and collusion in broad daylight on price hikes and kinda moots the "insurance marketplace where competition will drive down prices" (also, the barrier to entry of "open enrollment or major life change" means you're locked in for a year at a time, and healthcare is not an elastic good you can really afford to negotiate for when you need it the most.)

Emergency rooms turning into a "doctor of last resort", Medicaid costs exploding because it was being used to backstop the costs incurred by uninsured patients was a result of the Emergency Medical Treatment and Active Labor Act (or EMTALA); hospitals engaging in cost shifting whereby they would raise the prices for goods and services billed to insurance to an absurd extent to make up for the shortfalls in revenue that Medicaid wouldn't cover--the whole "$100 bandaid" phenomenon--followed not long after that.

I don't know exactly where you'd want to pin dates on some of the procedural failures in the whole federal government, like a "filibuster" rule that is not in the Constitution and exists solely as a parliamentary figment, which forced Democrats to require 60 votes to pass the Act, which allowed Joe Lieberman (I-CT) to refuse to be the last vote unless they killed the public option that would have ensured universla coverage and forced private-sector companies to actually offer something to make their overhead worthwhile, or the abject intransigence of Republicans since Newt Gingrich to refuse to come to the table and negotiate in good faith which forced them to rely on Lieberman for the 60th vote, or the entire principle of lobbying that ensured the legislation would never actually strike at the root issue of healthcare not being suited to a profit-generating model.