Mythical/Epic:
* The Azure Steppes
* The Whispering Windlands
* The Shadowed Plains
* The Valley of the Wild Stallion
* The Kingdom of the Silver Mane
* The Sunfire Herd
Nature-Inspired:
* The Mustang Dominion
* The Thunderhoof Territories
* The Wildflower Pastures
* The Canyon Run
* The Riverlands
* The Whispering Woods
Mysterious/Intriguing:
* The Hidden Herd
* The Forgotten Valley
* The Shifting Sands
* The Obsidian Hills
* The Crimson Dust
* The Midnight Herd
Powerful/Fearsome:
* The Iron Herd
* The Thunderhoof Empire
* The Burning Mane
* The Stormwind Kingdom
* The Iron Mountain
* The Whispering Storm
Bonus:
* You can also use the name of a famous wild horse breed, like "The Mustang Kingdom" or "The Przewalski's Domain".
* Consider the specific characteristics of your wild horses - are they strong, swift, cunning? Use those characteristics to inspire a name.
Remember, the best name will depend on the overall tone and theme of your story or world.