After the orcs ransacked the city a large horde of rohirrim charge in to the ranks of the weakened orcs. While focused on minus tirith the orcs were not expecting an attack and their army was almost destroyed.
A small group of ithilien rangers have came from the woods to help as gondor was once their home. Aragon will keep the orcs at the docks distracted as he arrived in an enemy boat with a huge army of warriors who have come to complete their quest, to defeat the armies of mordor and be free of their curse.
You must remain ever vigilant as on the way aragon saw a huge army of haradrim marching their way to gondor. Make use of your men and try to kill the orcs before the haradrim arrive.
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There are very few archers so protect them as you need them to kill the crossbow on the walls of osgiliath.