Gondor's Conflicts in the War of the Ring

The Conflict

Prelude

Now, lets turn to the Gondor Front. In the years proceeding the march on Minas Tirith, Gondor would be facing an uptick in Southron and Corsair raids. This would induce a bit of a crisis in Gondor's political establishment. First off is the problems I mentioned in the main section dealing with the Gondorian government. Namely, the reduction of legitimacy that would come from the government's inability to stop them. Local lords would likely take matters into their own hands and Minas Tirith will be exposed to internal revolt from the Southern Fiefs.
One of the major elements of the crisis facing Denethor is financial. The reliance on Southrons to man the southern border walls will at this point begin to backfire. They will desert their posts and actually attack Gondor in this region. So this region will see a major loss of manpower. Even worse is the former garrisons would be letting the enemy through the walls and using their knowledge of Gondor's terrain and doctrine against it. So something would have to give.
Given what we know about Dwarves, a default of Gondor's debts or asset seizures is likely to mean conflict between the Dwarves and Gondor. Knowing the state of Gondor's finances and desperate situation against Mordor, such actions would likely be taken. This would primarily be with the Lonely Mountain, as it looks to me that the Lonely Mountain would be the only dwarven kingdom with the resources at the right time to invest. Gondor's needs would be great - so the Iron Hills and Blue Mountains would probably not have enough to overcome the shortfall. Moria would not have been reestablished until to late.
For a government that uses the Economic Hit Man model, this would be a golden opportunity. The result here is that the Lonely Mountain would have a foot hold in which it can pour its money into. But a financial crisis would quickly develop that Gondor would find it difficult to escape. I would hardly blame Denethor if he chose to prioritize the military threat of Mordor over the financial threats of the Lonely Mountain. But the financial issues do need to be dealt with. So in an attempt to solve the financial issues, I suspect that he would seize the assets of the local dwarves and default on his debts to the Lonely Mountain. Possibly even start seizing the assets of nobles in a way that crosses the line. So this will make revolt by the nobles an even stronger possibility at the same time that the Lonely Mountain would have a mounting list of grievances.
If we remember, the second stage of the Economic Hit Man model is actually a coup or assassination aimed at the replacement of the top leadership. Some internal support for the replacement needs to be present in order for the replacement to remain in power long enough for the dwarves to get what they want out of it. This is where the united front with the angry nobles becomes vital. Again, Aragorn would prove to be an ideal candidate here. He has connections with the dwarves via Gimli at the very least. He also would have growing influence over the nobles due to his actions against the Corsairs in the march to Minas Tirith. So Aragorn would be able to unite the two forces.

Deployment

The result would have to be increasing the size of the military to compensate. But this will impose problems. The numbers that I come up with suggest an expansion of the Gondorian army by an equivalent of 25% of the prewar army. But this would be difficult to pull off fast enough due to the need to recruit and train that many extra men. That would pose significant financial problems for the government on top of being slow. This speed would further cause the legitimacy crisis to get worse as the attacks continue. The logical result would be dwarven mercenaries. But this would be even more costly as mercenaries tend to be quite well paid compared to normal soldiers. Which would fuel the issues surrounding the Lonely Mountain.
This would then allow for an alliance to materialize between Gondor and the Dwarves. I would expect the Lonely Mountain to want to preserve its investments. Remember how the nobles would be needed to keep Aragorn in power long enough for the Dwarves to recover their losses? The same goes for defeating Mordor. If Minas Tirith falls, getting Aragorn on the throne would be meaningless. Therefore, Aragorn would be able to leverage this to get the main armies of the Lonely Mountain to send reinforcements. This in turn would provide a strong justification for the Easterling attack on the Lonely Mountain that was absent in the canon story.
Minas Tirith would be a solid case for intervention by eagles given the fact that Sauron is such a clear and present danger to everything. I doubt the eagles would take part in any of the fighting against the Southrons and Easterlings after Sauron is defeated. However, before then they would have every reason to fight anything allied with Mordor. This means bombing attacks on the Easterlings and Southrons as they march to the black gate. The army marching to Minas Tirith would have to cross rivers – a perfect opportunity to strike from the air. Destruction of bridges would greatly slow their advance, and in the camps that result would leave them vulnerable as well. Then, when the catapults and siege towers are into place, they would be exposed again. This would be brutal for Mordor, though this army would not be as easy to destroy in a single blow as was Isengard. It would be quite exposed to attempts by the eagles to degrade and destroy their fighting power.

The Engagement

Also important is this conflict with the Lonely Mountain would probably not be outright war. The first step would be the covert actions and economic war. The first step would probably be sanctions on Gondor's trade. The mercenaries manning the southern border wall would be recalled. Depending on the severity of the Lonely Mountain's anger, they might be granted letters of marque and authorized to begin sounding out dissident groups to support. Their ultimate goal would be to move up to Minas Tirith and replace Denethor.
But with who? Well, probably Faramir. He appears to not have much of a reputation for having a strong will. Given his rejection of the One Ring, this is not entirely justified. But the reputation is still there. Plus, his posting with the Rangers was intentionally done to weaken him politically. Which means if he was installed, he would be dependent on the Lonely Mountain for power. Thus his compliance would be easier to secure. Boromir I suspect would be too popular, has too big of a local power base and is too strong willed to be controlled effectively.
Aragorn would become increasingly important later as he moves into the Southern Fiefs. This is where he would get most of his domestic support. We also have to remember that Moria would be his main backer while the dwarven interference would primarily be from the Lonely Mountain. As the battles rage on Aragorn would become an increasingly attractive candidate. Over time, he would see noble support increase and be better able to make the argument that he, not Faramir, would be able to get the dwarves what they want. Which means to me that Faramir would probably be the steward at the time of Minas Tirith. But he would then be gently warned that stepping down in favor of Aragorn might be a good idea after the Battle of Minas Tirith.
But there is a major issue here. These mercenaries would likely fail. In no small part this would be because of the elves present. The tower guards would also be in the way. Finally, the tensions would be high because their abandonment of the wall would essentially be the same action that allowed the Southrons to invade. Their actions would also have been reported to Minas Tirith before the dwarves or Mordor's armies do. So it is highly unlikely they would be allowed in. Nor would they likely have the force needed to force their way in.
The result is them setting up camp and figuring out a game plan. They would probably attempt to negotiate with the Gondorian government some sort of resolution. For this, they would probably be allowed to enter the city. However, not past the main gate into the "Gate of Jesus" stand in that allows for traffic between the government areas on the mountain and the civilian areas on the plain below. But more importantly, war is brewing with Mordor. Denethor would be too busy dealing with that to deal with a group of dwarves he probably doesn't trust.
So a high ranking official would be sent to conduct the meeting. They would probably have a 60 tower guard contingent as escort. This would be the full group typically reserved for the Steward and the cavalry group that are part of battlefield cohorts. The idea here is that this would allow a team of 12 officials to be sent with their full protection. The show of force and pomp surrounding the ceremonial and elite troops of Gondor would hopefully have an intimidation factor. Plus there is the suspicions on both sides. Gondor would expect trouble and send the tower guards for when the fighting breaks out. The dwarven team would probably consist of the officers and a few of the rank and file. I suspect their total would be 100-150.
But these negotiations would probably end badly. Gondor would probably be run by anti-dwarf sentiments that get in the way of them making reasonable concessions. This is not unheard of in history. The Russian government actually suffered supply issues and and defeats during World War One in part due to the Antisemitism of the government. The dwarves would also be on edge. Gondor has taken hostile actions against dwarven civilians. So these dwarves would be suspicious too.
The result would probably be the dwarven raiders getting insulted by the bigotry of the Gondorian negotiators and feel frustrated at the lack of progress. After all, they are trying to deal with crimes against fellow dwarves. The Tower Guard would be killed and the gatehouse seized. The negotiators would probably be held as hostages to compel concessions.
This would immediately be demonstrated as a bad idea. The full force of the local Gondorian forces would not be held back. The dwarves outside would try to flee, but anger would be boiling over. Looting, burning of buildings and massacres of civilians would probably occur. The Urban Cohorts would be the main force ready to deal with this. What amounts to a huge race riot would essentially have broken out. The Dwarves on one hand would be battling the local law enforcement as troops are called in as reinforcements.

Outcome

This would do massive amounts of damage. Though mainly to the civilian areas. I doubt the Gondorian military would take too many losses. Well, not enough to reduce effectiveness against Mordor. Secondly, the main body of dwarves would have some hope of getting out. So their objective would be to do as much damage as possible as the flee. Not to take and hold territory. The ones in the gatehouse would be trapped and slaughtered down to the last one. No mercy is likely.
At the same time, the civilians would probably and understandably find this a bit provocative. The down side of that is their own atrocities would follow. Dwarves would likely face race riots across Gondor. Lone dwarves would probably be lynched, shops burned and houses attacked.
Effectively, it would take something powerful and dramatic to avoid war between Gondor and the Lonely Mountain at this point. It would take time for the remnants of the dwarves to get back. They would naturally have news of what happened. The Lonely Mountain would then begin mobilizing troops for a full scale invasion of Gondor aimed at regime change. Faramir taking the throne would probably not be good enough for them anymore.
But something suitably dramatic would occur. The Easterlings would be on the move towards the Iron Hills. Mordor would be attacking Gondor at the same time. Aragorn would be moving up to Minas Tirith in what would ultimately put him on the throne. This would stop the Lonely Mountain's armies while also removing the regime hostile to the Lonely Mountain. In its place would be a figure already liked by the dwarves. Which means they would probably moderate their position enough to give Aragorn a chance.

Included Conflicts

• Assault on Osgiliath