100 modern day fully-equipped US Marines (without heavy armor, air support, nukes, etc.)
vs.
5000 fully-equipped WoW era Alliance Military (not players). So mostly regular infantry, marksmen, cavalry, mages and healers. Occasional other classes.
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The battle would take place in mountains. Marines have the first move.
GAME MECHANICS DO NOT APPLY.
Bullets kill just like in real life. Healers can heal non-fatal gun wounds, but they can't just stand in place and spam holy light, making anyone who doesn't instantly die invulnerable. Reviving is impossible. Rogues can't magically go invisible in the middle of desert. There are no levels or damage points. 40yd range limit is gone, etc.
Magic users are not omnipotent demigods. They can't just make themselves invulnerable or kill all the marines with a single spell. They're just regular Alliance footmages capable of casting Fireballs, Firebolts, some simple AoE and utility spells.
Who wins?