The Iroquois allow you to train Tomahawks and Mantlets out of your Barracks and Forts like regular units.
—In-game description

Iroquois League is a technology in the vanilla Age of Empires III that can be researched at a Trading Post built on an Iroquois settlement. Once researched, it allows Iroquois Tomahawks and Iroquois Mantlets to be trained at Barracks/Blockhouses and Forts.

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