I have found no evidence that states exactly what threat Anderson was afraid of. No person, persons or unit is named. At the time of the evacuation the fort's weaknesses had been mostly corrected; sand removed clear zones of fire established, and extra defensive measures made. Anderson, it seems, was talked into or lost his nerve into evacuating and burning the military stores and guns carriages at Fort Moultrie; clearly without official orders or clear authority to do so. Anderson was not threatened by any single group or action, his actions were premeditated and carefully planned days before he secretly moved his command, which brings into question why he didn't seek permission before he moved. His timing was also clearly meant to disrupt and cause the failure of the representatives of South Carolina meeting with the President of the United States to discuss a peaceful solution.
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David Upton