> The US can barely afford to school its children, purchase its homes, or enact reasonable public health measures without bankrupting people.
I think its pretty obvious to anyone whose knowledge of US history extends earlier than the 1960s that it did not start there (and, also, that the existence of the culture war and partisan polarization, while not unrelated, are quite distinct.)
> The problem is, the internet, the web, and now social media has accelerated this divisiveness to a whole new point
No, its not, as looking at US history anytime outside of a partisan realignment will show. Partisan polarization is a feature of the divide between the major parties in the two-party system aligning with the major ideological divides in the country, which they tend to do in a normal stable political alignment, but not during a period of partisan realignment.
The relatively low level of partisan divisiveness (despite the often quite high level of ideological divisiveness, seen in overlapping things like the Civil Rights Movement, the Anti-War Movement, the youth counterculture/“hippie” movement, etc.) in the (roughly) WWII to 1990s period isn't due to some kind of weird temporary absence of technology needed for partisan division, it is due to the long and overlapping partisan realignments spurred by (mainly) the New Deal Coalition and parties settling out their positions on civil rights. These things meant that on the politically salient ideological issues, the divide between the parties was not aligned with the major cleavages; “liberal Republicans” were farther left on the key ideological issues of the day than “conservative Democrats”, and the opposing ideological factions were present in both parties.
That political realignments had largely settled out by the mid-1990s, with Clinton and the remaining “conservative” Democrats who hadn't defected to the Republicans solidly to the left of what was acceptable for Republicans, and vice versa, which enabled ideological division to translate more directly into partisan division.