First come the historians and then, increasingly, come the game designers: the second waves to break on the shorelines of our recent history. Just so long as that history's violent, obviously. Just so long as it has options for cover systems and alternate fire modes.
Treyarch's reached the 1960s. Actually, it's reached the Cold War in general, with a plotline that spans decades as you witness the birth and evolution of the Special Forces through a series of deniable operations filled with secret agendas and "unconventional weaponry".
At this week's Activision press event, the developer kicks off its presentation by showing a full cut of the teaser trailer - a trailer that suggests someone's seen Jacob's Ladder, as sun-bleached jungle shootouts are intercut with wobbly footage of something that looks like a military hospital viewed through a metric ton of Vaseline.
Betrayal is in, according to the voiceover, as are voiceovers, as this will be the first COD where the player character has dialogue. It's too early to say whether CIA LCD experiments are in (although a Treyarch take on Touch Fuzzy Get Dizzy would be wild) but during the extremely loud playthrough that follows, the developers demonstrate a single-player game with enough moment-to-moment variety to suggest it would be unwise to rule anything out.
With Infinity Ward's door swinging wide, Treyarch seems to be enjoying its time in the limelight: new level names are introduced with the gravitas of The Eagles announcing that the next song is Hotel California, while other members of the gaming press report that developer fist-bumpage was witnessed backstage.
This being a videogame as well as a full-blown cultural event, then, it's kind of pleasing to see that the first proper reveal of Black Ops involves an ice level and a fire level. Let's look at the ice first.
It's 1968 - not really, or I'd have quite a lot of bets to put on, and difficulty plugging my laptop in anywhere - and an American Special Forces division is deep behind enemy lines in the wilds of Russia. Snow falls, mountain ridges sparkle in the frosty sunlight: this is the Cold War at its most authentically chilly.
The level starts several miles above all that, however, as you find yourself stuck behind a shiny faceplate as a crewmember on an SR71 high-altitude reconnaissance craft.
Treyarch cuts the sequence down to get to the shooting, so it's hard to get a sense of how it plays, but it appears to be a neat inversion of one of the original Modern Warfare's most inspired moments, as you stare down into a grainy screen and place waypoints to lead a ground team past enemy patrols far, far below you.
In reality, the sequence is there to remind you how iconic this period is: the space race, sleek black spy planes, computers the size of refrigerators. If Treyarch takes care over the details - and it certainly seems to be doing just that - this could be every bit as enjoyable to buzz through as the dodgy War on Terror chic of Modern Warfare.
Before you have time to say, "Ooh, Bakelite!" we're out of the heavens and back on the ground, however, playing as a member of the insertion team as they work their way down a mountainside towards a military installation buried in a freezing canyon of rock.
There are guards to avoid, twisty paths to navigate, and - lovely - a scoped crossbow to wield. The curvy lens does a great job of picking out distant soldiers, and there's always something a bit special about shooting someone with a crossbow, isn't there?
The first of the Russian base's relay station wobbles into view, and a Treyarch designer, plugging away at the controls, demonstrates that you can either take it stealthily, picking off enemies from a distance, or switch to explosive tips, blow up a nearby munitions truck and watch as troops spill out from the surrounding hills to get a shotgun blast in the face.
Even now, though, the staging is everywhere, and it's very effective. Racing through a kind of military-grade parking garage, parka-clad baddies pop up from behind caterpillar-tread crawlers at just the right moment to send your Innocent Smoothie into your lap, while there's no such thing as a bunker door in this game which doesn't have someone waiting behind it wielding something sharp for you to avoid as you poke him in the throat.
The base cleared, it's time for a little rappelling down a cliff-side, and then - didn't see this coming - right through the window of a second relay station. After the fairly scrappy fire fights of the last few minutes, this is a condensed 20 seconds of focused murder as your allies rip into a tiny room filled with very chilly Russians, leaving just enough space for you to pop off the odd finisher.
Finally, it's a quick rolling rumble through chambers filled with old data reels and computer banks, before you scramble across a gantry just as it's being attacked with rockets, along a mountain ledge that is coming apart around you, and then off the end of the next peak to parachute to safety.
It's thrilling to watch, it's probably thrilling to play, and, yes, there's no avoiding the fact that it's scripted right down to the snowflakes.
As it is with the fire. It's still 1968, but we're now in Hue City in Vietnam. The place is in ruins: American choppers are blasting it heavily from the air, the buildings are in chunks, and the sky is red with flame.
The mission starts with a bit more rappelling - down out of a chopper towards a target installation in the streets below - but the whole process speeds up a little when the helicopter you're spilling out of takes a direct hit and starts spinning towards the ground, lofting you through the window of a nearby office block in the process.
What follows is a blast through the dilapidated building that is as brilliantly controlled as anything in the series. This isn't the placement pop-out of Time Crisis, it's more like full-blown staging than scripting, and as you move from one damaged room to the next, you pass plenty of memorable vignettes stuck in alongside the baddies crouched in corners and ready to give you a shock.
At one turning, a man frantically tries to break a window and escape; at another, a cowering local ducks with his hands up as the door splinters behind him. Your shotgun seems to fire some kind of napalm charges that erupt in nasty little puddles of explosive light taking out three or four enemies at any one time, and even the bloodiest of encounters has been tweaked for cinematic thrills, as VCs appear to have been positioned at the top of stairs just so their torn corpses can roll downwards in the most ickily pleasing of manners.
Out on the street, it's the same tightly organised chaos, if that's possible. Flames guide you through obstacles, and rubble forms convenient ramps between tumbledown buildings while gunships buzz through the scarlet sky overhead. And then it's over.
That sky, though: it's just enough to remind you of a famous moment from Call of Duty 4 - an incident involving a downed chopper and a mushroom cloud. In reality, all of Call of Duty's single-player is gradually becoming that famous moment - cinematic, controlled, exquisitely directed, but far too linear for some people's tastes. Black Ops promises to be an incredible first playthough at the very least, then.
Afterwards? Afterwards there's multiplayer.
Call of Duty: Black Ops is due out for PC, PS3 and Xbox 360 on 9th November.