History
Dr. Doom tricked Diablo into sending himself far into the future. This future was "decimated by eons of warfare". A barren wasteland for Diablo to rule over[1].
Later, when Lockjaw was startled by the Human Torch flaming up as he was teleporting, he accidentally took Crystal and himself to this future. Diablo managed to concoct some potions to put the Inhuman and her pet under his power, and used Lockjaw to teleport them back to the present[2].