[Kuruharan]

Just out of curiosity, could somebody point me in the direction of a reference that says that the Elven population was increasing or at least maintaining itself in the Third Age?

As for the armies marching from the Black Gate to join the army from Minas Morgul, note that there is no mention of Easterlings and Haradrim (with their handy-dandy oliphaunts in tow) marching from Minas Morgul. Indeed, I have a hard time imagining that Sauron would be able to keep anything but orcs there because Tolkien gives the impression that any men in the immediate area tended to go quite mad. Some troops came up from the south to join him, but it is likely that the large numbers of Easterlings and Haradrim that appeared at Pelennor were the same ones that Frodo saw at the Black Gate. Note Gandalf’s message to Denethor…

The isle (Cair Andros) has fallen. Another army is come from the Black Gate, crossing from the north-east.

Rinfanawen

think that the Elves went through the same decision as the Hobbits and the Dwarves of Middle Earth. The battle was being fought on Man's ground. The Hobbits, as they more than often chose, wished to ignore all business outside of the Shire for that main purpose. It was outside of the Shire. The matters did not concern them.

This battle was fought against the armies of Men and Men alone...aside from a few small Hobbits. The Dwarves were not there either, because the matter did not involve Dwarves at that time. We cannot put all the blame on the Elves just because they happened to be a stronger force. The Elves made their choice, and they decided that it was not their battle to fight.

While I understand what you are trying to say, and agree with it in a way, I also concurrently disagree with your statement.

It was not that Elves and Dwarves were indifferent to the affairs of the rest of the world. I think that Legolas puts it best.

’Now why did not we wish for some of our own kinsfolk, Legolas?’
Legolas stood before the gate and turned his bright eyes away north and east, and his fair face was troubled. ‘I do not think that any would come,’ he answered. ‘They have no need to ride to war; war already marches on their own lands.’

Everyone was under attack.

Next Point: While I agree with Gurthang’s overall strategic sense, I have to echo Tuor of Gondolin’s logistical considerations. I think that Sauron sent as many troops against Minas Tirith (both from Morgul and from the Black Gate) as he could afford to feed.

Third Point: I believe that there is a general misconception that Sauron’s strongest armies remained inside Mordor prior to the Battle of the Morannon. I think this may not have been exactly the case. Gandalf confirms that Sauron still possessed large quantities of troops at that time. My question lies in the area of what use Sauron was making of those troops. My understanding of the text is that Sauron had to essentially strip his land bare of troops in order to assemble the army that fought before the Teeth. My belief is that those troops were his garrisons and newly arrived contingents that had not been properly organized into a field army. While this may have created an army that was numerically greater than any other he put into the field; this was not a field army in Sauron’s original planning. It was an ad hoc amalgamation that Sauron gathered to meet an emergency.

This does not mean that I think that Sauron had shot his bolt in the war. It does mean that, conventionally speaking, the West had probably bought itself a respite of several weeks or even months by their victory at Pelennor. I think that Sauron would have gathered a new army (or two), but that would have taken some time. I also doubt that he would have stripped all his garrisons to do so. This brings the urgency (and brilliance) of Gandalf’s scheme to the fore. The last thing the West wanted was to have Sauron turn inward to regroup at that moment. By doing what they did, Sauron had to “empty his lands” and reduce his odds of catching Frodo and Sam (even though Sauron almost did without knowing how close he came.)

Final Technical Point: The troops that attacked Lorien came from Dol Guldur. Considering the fact that the troops that attacked the Woodland Realm were also from Dol Guldur indicates that (a) Sauron maintained a large army there (b) the Elves were not numerous in either place (c) all of the above. My personal belief is all of the above. I would assume that troops from Dol Guldur would qualify under the large umbrella of “armies Mordor sent forth” even though they were not arriving directly from there.