The Dark lord Sauron has brought his destruction upon Middle Earth. He attempted to use rings of power to seduce the lesser races of Middle Earth. In response to this, King Elendil forged an alliance with Gil_Galad (The Elven High King) and set about gathering forces for a war with the Dark Lord.
After much preparation they set off to to strike at Sauron before he could become stronger. They would strike at the black gate and on the plains of Gorgoroth, the two forces would clash in deadly battle.
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The Dark Lord has left Barad-Dur empty as he commanded all legions to enter the field of battle. Dark tidings come from Gorgoroth and our large force is being decimated. Barad-Dur is impenetrable but has only a token force left behind to defend.
Build up the garrison and await the armies of the last alliance and destroy the last hope for Middle Earth, only with victory here and now can we begin the conquest of the free peoples of Middle Earth.
We still have strong ties with the Men of Harad and Rhun, trade your resources with them as Mordor is a barren and desolate land and lacking in wood and fertile land.
If all seems lost, the Dark Lord may have to enter the fray of battle himself.
Tips
-Focus on economy right away, it will help later
-Harad may send some archers to aid you
-Use the surrounding resources to trade for wood and food
-Ensure the orcs have a steady flow of grogg, and build more temples of Morgoth to appease them
-Attempt V Hard at your own will, it's insane
The siege begins after 9 years, good luck.....