To my knowledge, this is the third Medieval American set released for Civ4, and it's based very heavily off of Zerver's American Medieval series (of which Zerver released two distinct sets, which is why I refer to this set as v3.0).
This particular set/release is based very heavily off of Zerver's initial v1.0 American Medieval set. Most of the tunics and unit models are from that set, though some tunics have been touched up, a new American shield added (based on the Great Seal of the United States), a couple of new models have been used (Maceman and Knight), and I've added a new American Medieval Warlord.
All needed files are included, as-well as a txt file listing the needed animations for each unit. This set includes 11 combat units and one warlord.
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American Medieval v3.0 2016-10-05
American Medieval v3.0