Gondor's Expansion

Now, reconstruction proper would require securing the borders of Gondor. This means at least some additional military actions to break whatever offensive actions the Southrons and Easterlins have in mind. To start with, lets look at what the balance of forces is at this point. Gondor is the major power on the side of the “free peoples of Middle Earth” with Rohan as their main ally. The elves and dwarves would provide supporting roles to this coalition. On the other side, there was the forces of Mordor (orcs and trolls) with the Easterlings and Southrons as junior partners. Though lets be honest here – that coalition is still powerful but much more fractured due to the loss of the Witch King in the Battle of Minas Tirith.
Now, the first thing that has to happen is the use of the critical phase here to secure the basics. This is when all the diplomacy takes place where Aragorn tries to get Rivendell to help him. It is also when the One Ring is the closest to being destroyed or right after it was – leaving the forces of Mordor at their most vulnerable. Troop deployments to Rohan would begin here as would the efforts to head off rebellions.
The defeat of Mordor as stated elsewhere would eliminate the main enemy fighting force and their leader. The geographic center of the coalition would also be occupied by Gondor. Which means that a united front between Easterlings and the Southrons/Corsairs would be practically impossible. But the feasibility of coordination is kinda irrelevant. The practical destruction of the Corsair navy and Southron Oiliphaunts eliminates them as major forces now. The Easterling army would be broken and their society descending into a civil war.
So – where now? This would grant great amounts of breathing space to Gondor and by extension everyone else it is allied to. But, Aragorn would be weak. He would need to secure his own power before being able to do too much.
To start with lets compare the two areas and cultures to see which is best suited for Gondor to make its main focus. To better do this, it would help to be clear as to Gondor’s war aims. Lord of the Rings seems to be a textbook example of an international order defined by Classical Offensive Realism. Realism is an international relations theory that sees war as inevitable. At a structural level, there is no body that can effectively mediate between powers. Rational and competitive leaders will respond to this reality by taking actions to maximize their own power as they see this as the only tool for self preservation. Low quality and quantity of information about the intentions and power of the other state will result in limited cooperation even against a larger foe. At best, states are obsessed with security and the territorial expansion that can provide a state’s needed security are constrained by outside powers. Lastly, realism is built on the security dilemma – actions taken to become more secure within one’s own borders can be taken by other powers as a signal of offensive intentions, thus provoking a counter.
The classical part is a school of realist thought that takes a very pessimistic view on human nature. Human nature is seen as flawed. This and the search for power by conflicting states is why classical realists see the security dilemma and war as inevitable. The offensive element is another subsection of Realism that posits that the goal of leaders is not security but power. Rulers will not be happy until they have a world empire basically. It is only the power of other states that stops this from happening.
So, how does this fit into Lord of the Rings? The closest thing that comes to the UN is the Council of Elrond. That is not quite an effective replacement. Sauron worked for thousands of years to take over the entire world and the entire international order that existed was designed to counter this threat. This is exactly what Realism would predict. Also, one of the key elements of Realism is the idea that states all have the same interests and will respond to the same conditions in the same way. Notice in Lord of the Rings all governments are monarchies with no hint of real dissent, all people obey and even the pastoral Rohan built forts and walls around their capital? That may have been a narrative device to make writing easier, but that also forms the same unitary “black box”.
Also important is the view of human nature in Lord of the Rings. All humans are seen as easily corruptible in the face of power. Isildur being the most obvious example. The lust for power is what leads the Ring Wraiths to take their rings of power. Aragorn expressed the feeling that the same lust for power is a form of family curse. Then add in what the One Ring really is – a physical representation of total power. Absolute power corrupts absolutely as the saying goes. So we can expect that the Ring would corrupt worse and faster than anything else. But that does not mean that lesser power does not corrupt at all. It may be less tempting, but the temptation is clearly there.

The Conflict

Prelude

Add in the natural impacts of mass mobilization warfare, the War of the Ring producing crisis after crisis for Aragorn at the same time it pushes him to the pinnacle of power in the human world, you can see how the corruption would set in. Keep in mind that what I have described thus far puts in Aragorn’s hands the beginnings of a modern police and army, both used to combat both internal and external forces as a means to consolidate control.
Aragorn might not turn into a Ring Wraith or Gollum, but the toll will be paid. We can expect that a war started for security could see Aragorn pushed to become a “power-maximizing revisionist harboring aggressive intentions”. Aragorn will “recognize that the best way to ensure security is to achieve hegemony now, thus eliminating any possibility of a challenge by another great power”.
What this also means is that the weakness of Mordor's remaining allies would be tempting targets. The Easterlings have repeatedly in the past taken the initiative in the past to launch rather brutal attacks on Gondor in the lulls where Sauron or Morgoth was not giving orders. We are talking pillaging and enslavement of whole cities – that sort of thing. Meanwhile, the Southrons are more tribal in their social structure – so a united front and quick mobilization is much harder. This means that the quest for the security that Realism suggests would be the main objective of states would motivate Gondor to first attack the Rhun.
But that is not exactly true. We have to remember that the civil war would have essentially broken any military threat coming from Rhun.

Deployment

Now, lets look at the two main rivals Gondor has left now that Mordor is basically crushed totally. If we remember from before, the Easterlings have a home population between 5,257,150 and 7,894,707 people and the Southrons are between 3,000 to 18,000. The Corsairs would have 16,936 and 25,404 freemen and between 20,878 and 23,798 slaves. This would seem to indicate that the Easterlings would be the bigger threat and should be dealt with first.
First, Gondor’s full strength has yet to be mobilized yet. This means that taking on its larger enemy would be probably a bad idea.

The Engagement

To make this resettlement secure, the first actions would be to send all available troops to occupy Osgiliath. Once the area is secure, I would leave 1,000 Urban Cohorts to protect the area. Another 1,000 I would send to garrison Minas Morgul. This should not be too hard, as the entire force protecting it would have been destroyed in the battle of Minas Tirith and invasion of Mordor. I would then leave another 1,000 Cohorts with Pelargir. The Tower Guard and reduced garrison of perhaps one Banda would be left to protect Minas Tirith. The forces at Pelargir would set up defensive palisades and earthworks around it to make sure it was secure for use as a staging ground for battles against the Southrons. This is about as good of a defense against them that I see at the moment.

Outcome

First, incorporation of Rohan firmly into the Realm would be relatively easy. The use of Moria’s reconstruction aid to finance the rebuilding of Rohan would go a long way to making the government dependent on Gondor. Aragorn did have daughters – which could then be married off to Eomer. Add in the Eowyn married Faramir and the two royal families seem to be merging. Then it is just a matter of promoting further intermarriage between the noble families. Once you get this set up, it should be pretty easy to put pressure on the Rohan to officially merge. Oh yeah, there is also the issue that Gondor has at least three groups of elite troops in and around Rohan that can cause serious problems if needed.
The last group that needs to be dealt with is the orcs. Apparently they are by their nature too violent to form more than tribal groups and live in underground caves. They also are known for their hatred of everyone and everything. Meaning they will not make peace. But they are also too fragmented to pose much of a challenge. To handle them, I think a bounty on orcs could be used. This would see many destitute people outside the army take up the profession of orc or troll hunter. Possibly 1,000 of the conscripts could probably be spared to move into the main core region of Mordor to hunt down and destroy the last few bands that escaped the main killings in battle. Now, I have no where near enough information to figure out total orc populations and thus how long this would take. But the main threat is contained with the occupation of Udun and Minas Morgul.

Aftermath

From there, things start to get messy. Two of the four newly acquired major areas part of the expanded Gondor (Rhun and Harad) have residents that had to be subdued by force in a full conquest. They have been long term enemies of Gondor, are ethnicly diverse, war like and have distinct appearances and culture. Part of this distinct culture is apparently worshiping Sauron.
Now, one of the features of both the reduction and encomienda systems is the attempt to impose the values of the colonizer (Spain in real life and Gondor in LOTR). The use of settlers in Rhun accomplishes the same task by literally replacing the local inhabitants with those of a chosen cultural or ethnic background. This cultural imperialism is vital for the security of Gondor in a post War of the Rings world. The history of Middle Earth, is defined by the survivors of the defeated big bad picking up where their former masters left off. Sauron was actually one of the lesser beings who sided with Morgoth – the original evil dude. Morgoth is described as the second most powerful being in all of Middle Earth’s history. Sauron was much lower on the food chain.
With the dragons, orcs and trolls mostly defeated and totally shattered organizationally, this leaves the Southrons and Easterlings to continue this trend, as I have discussed. However, they were pretty warlike and corrupted by Sauron. So, it seems that this hatred of Gondor and violent nature is not going away any time soon. This means that no mere military defeat is likely to be enough. Wounded pride and hatred of a long standing enemy will provoke continued struggles. This means that whatever Aragorn can do to attempt to break the long standing cultural allegiance to Mordor should be done. Outlawing the Black Speech and the local dialects, education aimed at promoting new languages and cultural norms, Gondor centric history and so forth should be implemented. Religion should be shut down as well where it venerates either Morgoth or Sauron.
The problem is that if we assume that they are not as violent and anti-Gondor as I present them, the act of colonization and conquest always provokes a backlash by the native population. I suspect that the end result ultimately would be a slow moving genocide. Think the US expansion and treatment of Native Americans. The escalation I mention in the discussion of the Rhun could play out in both places, leading to a form of reservation system as well. The Herero and Namaqua Genocide could also prove a more extreme model – where the inhabitants are driven into the desert after their defeats and trapped there. Death from starvation and dehydration was rampant. Those who retreated or tried to escape were captured and sent to concentration camps with the all to standard death from abuse, overwork and diseases that concentration camps are known for. Application of this model to Lord of the Rings is likely to see slavery put in instead of the camps. Slavery was also common in the ancient world and was the replacement for the encomienda system. So, should the Southrons not be driven into the desert to starve, they are still likely to be sold into slavery.