What would you classify the 80s, 90s, 2000s, 2010s, and 2020s as?
I haven't put the same kind of thought into it and don't have (ironically) as good of a feel for the cultural shifts.
I'd say that there are clear differences between America in our little End of History that lasted for basically the whole 1990s (and then up and died). That was probably the last decade where there were still lots of good movies; movie-making really aged fine in the 70s, 80s and 90s. It was the era of the blockbuster. Music started getting boring. Politically it was classical political correctness, which was easy to ignore unlike both the Long Seventies and Clown World, as it was more just a really gay, annoying type of nannying than the demon it became. The tone of the era was very optimistic. I said End of History for a reason, Fukuyama and the Neoliberal Fuckboys thought we had already achieved the Star Trek fantasy of world government forever.
Something does change between the Long Seventies and the Eighties (TM) with the United States coming out of its malaise and finding its balls. If you want, you could say that socially the Nineties really are just a continuation of the Eighties with a changing conception of the world (from a pop culture obsessed with Soviet invasions to glorying in our own victory). One thing both had in common was that you could have, like, a million gay jokes and you could say nigger while still paling around with your Burger King Kids Klub group of friends. (Real life was never that artificially diverse, but I think there was a very real racial detente.) The whole period was one of aggression abroad and detente/restraint domestically, and prosperity. The scariest thing is the Clinton Administration going on a rampage against militias, Waco, random jerks in the woods. You start to get the first real obvious signs of Leviathan using this espionage apparatus that was basically created to fight Red Scares and Cold Wars against H'White people (besides the buck breaking of the KKK). The War on Drugs starts getting really retarded.
Then we get the Long Naughts, or let's call it Super Bush World. Eight years of that, from 2000-2012. Libtards are obnoxious shrieking faggots (when have they ever not been?). Civil liberties are the major theme of the decade due to Forever War II and libertarians are probably (?) at the height of their influence culturally and politically. The overreaches of the govt prove themselves devastatingly true in Clown World. Culture War is a thing forever, but I think it starts to take its current shapes, its current front lines, around this time. The country goes from North-South defense (fuck the Blacks) to Everyone Detente to Blue-Black detente, fuck the Reds.
When does Clown World begin? Everyone on here says 2014, but I think that's from being chronically online. I get that there are arguments that many specific bad things happened around then, especially in nerd culture. I think it's a little mistaken to start the downward spiral right with the election of Obama, and likewise it's definitely too late to put it with Trump. I'm tentatively saying 2012 because that was when Trayvon Martin (who I hear surprisingly little about, these days, compared to Mike Brown) blew upon the horrorshow of modern day anti-White race pogroms. Literally nothing from the Summer of Floyd was new, just the sheer vigor with which they enforced it on everyone. What was shocking wasn't the same warmed over talking points, but the way people were getting sacked from jobs - fucking IDEOLOGICALLY PURGED by the private sector - over it, and the way it was used to push through a wave of iconoclasm.
In Stephen King's IT there is a town of Derry that has a cycle where, at regular (but not like clockwork) intervals the eldritch demon god of the town will emerge to begin preying on the townsfolk, and in each such era its insane energy drives the town to murder and other acts of violence and dysfunction, social breakdown, at a scale that would be incredible but for that IT has the power to anesthetize the population. Crazy things happen in Derry, but nobody ever seems to notice the sociological mystery at work there. That is like what the US has been operating on for at least 200 years. The earliest time I can point to as the American Spider God Cycle is the Great Yee-Yee of 1850-1880, ish, when the South and North went deranged; the derangement even spread West, by the end, with the post-Civil War flood of frontier violence. It broke like a fever in 1877 with the corrupt bargain, high tide of the revolutionary sentiment at the Homestead Strike and victory in the Indian Wars.
Then it came stalking again in Wilsonian America, year uncertain to me but surely hitting a sort of apogee in the insanity of World War I and breaking like a fever after socialist defeat (at the hands of progressives, Progressivism was an enemy to both Socialism and Populism) at Blair Mountain, 1921, although the social sickness carried on for a long time; you could perhaps even start it with Wilson's war and argue it breaks some time into the Great Depression with moral renewal of the country.
Then the Long Seventies.
Finally Clown World. And I think the fever broke with Trump's second election; the mood has shifted in a very perceptible, but hard to explain, way. But the progress of past cycles is never undone.
The Demon of Unrest (I just stole that name for a book title) is the same creature every time. It changes its outward ideology; sometimes it masquerades as limited government, sometimes as unlimited government. Sometimes it comes from the South, sometimes from the North. Sometimes it preys on White people's worst natures, sometimes on Black people's. Sometimes it even expresses itself through both times, as I'd argue it did in the Civil War era. But the consistent thing about it is that it is the rich using sectarianism - usually ethnic - to derail populist movements and anything that threatens to encroach on entrenched power (corporate and govt). I don't think my model actually fits the Long Seventies well, compared to the War between the States, WW1 and aftermath and Clown World. Before the War between the States it is hard to defend it; maybe the desperate power-grabbing of the Federalists (Adams' attempts to play dictator, the War of 1812 bringing things to a head with these traitorous mercantilist shitbags), but I don't see the telltale signs of race war propaganda there. I suppose they hadn't figured it out yet. Federalists hadn't yet pioneered the use of race to divide, while in the Seventies it was foreign actors (Soviets) and a newcomer (Jews) to the American stage that were acting disruptive.
Edit: My silly names for it, some stolen from books I like or at least tolerate:
A Disease in the Public Mind (1848-1877)
Yankee Leviathan (1877 to somewhere around WW1 or the Progressive Era)
A Fever in the Heartland (no later than 1908 through no earlier than 1921)
Mister Roosevelt's Wild Ride (Great Depression, WW2 and Korea)
Jukebox Jubilee (the Long Fifties)
Days of Rage (the Long Seventies)
End of History (1980s-ish to 2001)
Super Bush World (2001-2012)
Scratch that, I'm going Bush World Adventures, that one's more fun, look it up.
Clown World (2012-present)
(End of History should be taken with the sardonic tone of "War to End All Wars.")
I likewise like to historiographically divide the US into three movements of itself based on its self-conception:
First America (voluntary confederacy of states)
Second America (imperial power of the North, a Euro-American nationalist state)
Third America (diverse bullshit "civic nationalist" America, starting from the Civil Rights Act and that immigration act that JFK, I think, passed, allowing non-Whites in in large numbers)
Edit: Each historical turning in America's self-conception comes from the Demon of Unrest cycle. Civil War mortally wounded and WW1 curbstomped to death First America. (Wilson kind of does it by, like I said, bringing the South into the fold... had to colonize it to pass through the first stages, but had to get its cooperation for the last stages.) Long Seventies gets us Third America.
So what do we see today? Will Clown World end with Third America solidifying, or will it prove a temporary aberration, a launching point for disunion or revival?