afroakuma's Planar Questions Thread! (You ask, I'll answer)

[Eldan]

Invasions (both successful and failed) of the Prime Material Plane by exemplars and other planar races are well-documented in D&D. However, what I want to know is if there's ever been a significant invasion of a plane (or layer of a plane) by Material forces. Was it successful, if so? What would it take to establish significant control over a planar layer by Prime Material forces?

There was the War of Iron. When the Harmonium had pacified it's home planet of Ortho, they decided the next step to bring Harmony to the planes was to invade the Abyss.

They failed rather miserably.

But then, the planes were never a main focus for Ortho.