"The Horde" was a Boxed-set campaign setting for D&D, released by TSR in 1990 to add Mongolians (called the Tuigan) to the Forgotten Realms. The boxed set describes the area known as the Endless Wastes- you'll generally find it in the far north-east of your maps of Toril.
The boxed set describes a range of cities, cultures, and customs, including water-breaking-rock style kung fu, a Great Wall with the bound soul of a dragon desperately trying to escape, and most importantly rules for the Shatjan - a race of short half-men with the head of a reindeer, who eat grass and have an icy breath weapon. It also includes stats for Yamun Kahan, a red-headed brutal nomad warlord who is both a brilliant strategist who has united the clans.
Apparently Genghis motherfucking Khan was a L17 Fighter.
|Dungeons & Dragons Campaign Settings|
|Basic D&D:||Mystara (Blackmoor) - Pelinore|
|AD&D:||Birthright - Council of Wyrms - Dark Sun - Dragonlance |
Forgotten Realms (Al-Qadim - The Horde - Icewind Dale - Kara-Tur - Maztica)
Greyhawk - Jakandor - Mystara (Hollow World - Red Steel - Savage Coast)
Planescape - Ravenloft (Masque of the Red Death) - Spelljammer
|3rd/3.5 Edition:|| Blackmoor - Dragonlance - Eberron - Forgotten Realms |
Ghostwalk - Greyhawk (Sundered Empire) - Ravenloft
|4th Edition:||Blackmoor - Dark Sun - Eberron - Forgotten Realms - Nentir Vale|
|5th Edition:|| Dragonlance - Eberron - Forgotten Realms - Greyhawk |
Nentir Vale - Ravenloft - Ravnica - Spelljammer
|Third Party:|| Dragonmech (3E) - Dragonstar (3E) - Kingdoms of Kalamar (2E/3E/4E) |
Midnight (3E/4E) - Ptolus (3E) - Scarred Lands (3E/5E) - Spellslinger (3E)
Wilderlands of High Fantasy (Basic)