Azeroth
Mythical weapons:
- Atiesh
- Ashbringer
- Thunderfury
- Shadowmourne
- Quel'Delar
- Glowing Brightwood Staff
Equipment:
Everything that Iron Horde have, and more
Races:
Everything except Gronn and Ogres (ok, one advantage there), if you count size and brute strength alone.
Magics:
Everything they have to the power 10. Warlock magic beyond anything Gul'Dan has knowledge of. Shamanism with 30 extra years of experience. Mages, Priests, *shudder* monks, druids.
Heroes:
Beyond counting
Experience:
30 years of warring against anything from your lowliest Murlocs to not fully powered Kil'Jaeden and Old Gods.
General army equipment materials:
Light years beyond what we had for Orcs and Humans and Warcraft 2. Ele-freaking-mentium.
What does Iron Horde have to oppose all that? A bunch of guys experienced at war by ages of war and training. That's great, so were the Samurai, but we all know what happened to them. Japanese steel doesn't parry bullets.