Answer: Tallow trees (Sapium sebiferum) are somewhat short lived (about 20 years). If your trees are much younger, the cause will likely be found in the root system. Such sudden death is a sign of a major collapse of the plumbing system of the tree. The tallow has few insect or disease problems. Nevertheless, something has shut down the root system.
I would suspect cotton root rot, but other root diseases are possible. There is no treatment or cure for most of these organisms. Unfortunately you are left to "wait and see". You can watch the base of the tree for mushroom growth or a white mat of fungal fibers under the bark indicating a root rot organism.
Another possibility, although a bit unusual, would be a gas leak underground or damage from a herbicide.
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