I would agree that Hobgoblins are the most likely, but technically there's no particular restrictions on any of the races having spellcasters, it's just that Goblins and Kobolds are not inclined towards straight fights or fighting above ground, Bugbears, Gnolls, and Lizardfolk are on the primitive side, Orcs are generally a bit more disorganized than that, and most of the remainder are either on the uncommon side or don't tend to live in the same territories humans, though Sahuagin and Yuan-ti are possibly interesting variant options, and you could always just pick a race that seemed interesting and declare that in your setting they're a bit different.
Drow, Deep Gnomes, Evil Dwarves, literally any race you want to be set-up the way you want it to be in your world, other humans (you ever notice how well different cultures/religions get along here in Earth historically?), Tieglings, Dragonborn, sentient undead, shadow halflings, half-elves, who are parishes by both human and elf communities, and fight for equality or dominance.
The list is limited only by your imagination and work ethic.
I'm looking for a smart race of monster that that would be at war with men and elves.
Smart enough to construct military outposts, have spell casters, forges and armories, but not so clever that they would easily out smart my PCs.
I'm relatively new to the game, so any ideas would be appreciated.
Hobgoblins are probably your best option. They're very intelligent and tactical, with a strict military hierarchy.
Wizard (Gandalf) of the Tolkien Club
I would agree that Hobgoblins are the most likely, but technically there's no particular restrictions on any of the races having spellcasters, it's just that Goblins and Kobolds are not inclined towards straight fights or fighting above ground, Bugbears, Gnolls, and Lizardfolk are on the primitive side, Orcs are generally a bit more disorganized than that, and most of the remainder are either on the uncommon side or don't tend to live in the same territories humans, though Sahuagin and Yuan-ti are possibly interesting variant options, and you could always just pick a race that seemed interesting and declare that in your setting they're a bit different.
Drow, Deep Gnomes, Evil Dwarves, literally any race you want to be set-up the way you want it to be in your world, other humans (you ever notice how well different cultures/religions get along here in Earth historically?), Tieglings, Dragonborn, sentient undead, shadow halflings, half-elves, who are parishes by both human and elf communities, and fight for equality or dominance.
The list is limited only by your imagination and work ethic.
Is your game set in Faerun? If so what region?
I think it's more involving if it makes sense with the surroundings of the adventure.