An Iroquois army tends to be more varied than the other Native Americans, since they can use infantry, cavalry and artillery in their attacks. They are more like Europen civilization than the other native civilization.
The Iroquois siege is effective; the Ram can reduce a town to rubble, the Mantlet has enough hit points and resistence to act as a screen, and the Light Cannon is good against both units and buildings. The Iroquois deck has a few cards that can improve their already-impressive siege weapons.
The Iroquois forces suffer from two glaring weaknesses. The first is their cavalry, which is quite unimpressive, meaning that they're doomed to either be slow-moving or weak.
The other is their navy, which not only lacks anything to match the heavier ships, like the Aztec Tlaloc Canoe, but they are also the only civilization to lack the Admiralty card - meaning that their navy will most likely be smaller than the enemy force. A few Privateers, combined with the Water Dance from the home city, can be the rescue.