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human
[Lord of the Rings] If Aragorn had kept the Army of the Dead, would any force in Middle-Earth have been able to stand against it?

Seems like there'd be nothing to stop Aragorn taking over the world if he wanted to seeing as only he can block their attacks. 

Edit: Thanks for the detailed answers, guys.
gpt
They did still retain the free will to choose to assist Aragorn due to his promise (inferred or otherwise). Would think quite the opposite would have happened at Pelennor fields if he did not release them. The parried strike by Aragorn only served to prove his lineage, not that he could not be defeated by them.