system
Given the following post, respond as if you're commenting on Reddit:
human
[Lord of the Rings] Could they recreate the Army of the Dead by having people voluntarily break oaths?
gpt
No. 

1. It wasn't the fact that they broke their oath that turned them into undead monstrosities. Isildur's curse did that. 
2. Humanity just doesn't have the power to do that anymore by the time LOTR's story starts. The world's magic is fading, Humanity's power is fading, Everything in Arda is slowly progressing towards becoming completely mundane (as, remember, It's framed as being our own world, just before). The Magic necessary to do something like that again simply doesn't exist, unless maybe you're an ancient and powerful Elf Lord, one of the Istari, or Sauron himself. Maybe the Witch King could have done it.
3. Even if that magic *was* still accessible for humanity, It's not entirely clear how it actually worked. LOTR and its associated works don't really describe the rules of magic very clearly (what we call a soft magic system). It's entirely possible that such a curse would require the proper emotional state, or even outright malice, to accomplish successfully, which provides a further barrier to doing it on purpose.