The Infernal Generals
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Demons! Creatures from myths and religions, which actually existed in other planes of existence, Dimensions.
The Infernal Gates that led to the Dimension of Demons connected to several other dimensions which had a close connection with it, however, there was no such thing as a connection to this dimension within Earth's dimension.
Nonetheless, when the Dimensional Convergence happened, Demons leaked into Earth just as much as any other entity from other dimensions.
The World of Demons had only sent a few armies of their lower ranked and lesser demons to scout the area, only to find that powerful groups of entities had already sent their own scouting teams, such as the Slarkobs and the Celestials.
Due to this, the powerful Infernal Entities that existed in this world had been wary of them, and had only pretended to have sent some swarms of demons as wild monsters than anything else.