X4-5-10: Desert Nomads series
The Desert Nomads series is an Adventure Path for the original-ish Dungeons & Dragons ruleset by Tom Moldvay as revised Frank Mentzer. The modules are X4: Master of the Desert Nomads, X5: Temple of Death, and (after a two year delay and four module gap) X10: Red Arrow, Black Shield. The setting is the Known World soon to become the Mystara setting, after this series broke it. Series shunned by normies for its supposed 'phobia. On that, well...
The first two were David/Zeb Cook, intentionally. The third was Michael Dobson, picking it up again.
X4: Master of the Desert Nomads
Darokin and the Nomads are at war, and the party is in the reserves at Pramayama between them at the edge of the Desert of Sind. The setting hadn't made anything of this region yet. Zeb (the lazy) had the opportunity to sketch out a measly paragraph on fantasy Punjab, but didn't. Later Mystara supplements will do this, like the Voyage of the Princess Ark. But anyway.
Here the party wanders through the desert, following the spoor of the army. X6: Quagmire! has additional detail on the desert, if you like. It's a harsh one.
Darokin's army - get this - has been TPKed. Turns out the nomads have a Master now, presumably not the same Master as Blizzard Pass (ohhh, Zeb). Now the party has to switch gears from "warriors" to "assassins". They're already deep in the desert, so there's no point in turning back; they gotta cross the Great Pass to knock out the Master where he lives. They get to the foothills, controlled by an abbey whose masters are some strange lycanthropic/undead humanoids called "bhuts".
Ten year olds find that name hilarious. So will players, when they find out that bless on a weapon does instakill on them. Nice monster design, bhuthead.
It's got new monsters, like those bhuts. Also the Tabi, an Islamic name like Qasit; and the nagpa treated like a badly energy-drained vrock.
X5: Temple of Death
The party finally gets through the Great Pass, entering the land Hule. Hule is as expected a theocratic dystopia, but here Cook backed off the Islamic(ate) themes. Hule's elite is more Merkabah Judaism if some qabbalist actually succeeded in contacting the Elder Gods... with a side order of Plato. Some towns are dotted on Hule's side o' the map but have no names (Slagovich has a name, but that's for Coming Attractions in X6). Whatever town you enter first, that one officially becomes "Magden" and takes the Magden town map. Really, Dave?
X5 offers five new monsters: the proto-Last-of-Us dusanu, the turtle-jawa geonid, the malfera who's awesome, the
X-series doppelgangermujina who earns Cook (the lazy) an atomic wedgie, and the spectral hound. The Companion Set let in the last three, skipping the dusanu and the geonid.
The Master's name is revealed - Hosadus; his citadel is done up like a chariot. In a theme lifted from X3: Curse of Xanathon it's not easy to kill this guy.
X10: Red Arrow, Black Shield
Did the players ever wonder: hey, the X4-5 backstory sounds better than the actual series, I'd rather role-play how Darokin fights this war. Here Dobson grants them that chance... and himself the chance to sell BATTLESYSTEM!! boxes to a new corner of TSR fandom.
This module starts by running the party off the bordertown Akesoli - no Pramayama for them, the Master's punch hits right at home. Darokin knows it hasn't a chance especially once totally-not-Arab nation Ylaruam sides with its fellow(?) Nomads. So the party must roam the Known World convincing other nations to join the fight. There are tie-ins with earlier X-series modules that the party can play, especially down in Minrothad and Ierendi. (For the former, X8: Drums on Fire Mountain is transferred from Thyatis, likely to push the party toward doing... other tasks for Emperor Thincol. For the latter, righteous shade is cast upon the XL "series".) The module has a subplot whose settings, by coincidence, contain fragments of a Crystal Dagger Of MacGuffin. Gee, wonder how that'll work?
The players can have the party - if close enough - participate in some of the battles, as leaders and/or heroes. Here are Companion Set war-machine stats and those BATTLESYSTEM encounters. There's also a flowchart-system for travelling cities at a pinch, the Chase Flow Chart: which saves time exploring a massive map if the party's just there for one simple task. Like running like a rabbit OUT of the map.
The artwork is notably bad: some cribbed from X3: Curse of Xanathon; some just from the headlines. I mean seriously, check out Hosadus. It being 1985, there was some level of anti-Khomeinist sentiment in Western countries.
This series, the World War of Mystara, visits mayhem upon the Known World. It's basically the module you run to make the Known World uninhabitable, so the party has little choice but to sail off to Norwold instead, to start CM1: Test of the Warlords. As it happens the Thyatis subplot here sets up exactly that.
But, like Tolkien's "The Fall of Gondolin", in the meantime X4, X5, and X10 had all expanded the available lore for all the nations that DIDN'T get jihadded. Players wanted to learn more about them.
So the Gazetteer series retcons at least X10 two hundred years after all the other modules. That's "1200 CY" in Gazetteer / Mystara parlance. Of course that means the human mortal kings here probably aren't the same kings in the CM1 timeline.
And then Champions of Mystara: Explorer's Manual (1993) re-retconed "1005 AC" (same as CY). Allahu a'lem.