The Principality of Harondor
Harondor isn't the smallest faction, nor the faction with the poorest lands. But its strategic situation and tactical options make it my candidate for the faction with the most difficult start in Dominion of Men.
To see why this is so, you need first to take a look at the campaign map (there's a screenshot of the WIP starting positions in the screenshots thread). Harondor is sandwiched between the Empire of Harad and the Kingdom of Adunabar, with its next-nearest neighbor being the Reunited Kingdom across the mouths of the Anduin. Put plainly, this four-province faction begins play surrounded by the three largest factions on the map – with no nearby rebel-held provinces for easy picking. You know how with most factions you can do a little light conquering in order to establish yourself before going after the bigger threats? Not an option. Right out of the gate, Harondor must decide which of these behemoths to strike – if the Principality manages to strike first at all.
Secondly, consider that the troops available to a Prince of Harondor are essentially the Haradrian types, with a strong presence of plainsmen (the skirmishers and mounted skirmishers) and some heavier-armed swordsmen. Harad can make good use of the basic Southron roster because the Empire can afford to produce them en masse (as anyone knows who has ever played as a Dunedanic faction in TNS. Plus, Harad can train Mumakil...). Harondor, thanks to its connections with the nearby Dunedain, can construct some small-scale siege engines, but otherwise must largely rely on its relatively fragile infantry and skirmishing cavalry in the early years.
“OK,” you think, “the land game looks pretty hopeless. No problem – we've got boats! I can just migrate to better pastures.” Well … maybe. Although Harondor does have access to the Sea, the much larger navies of Harad and the Reunited Kingdom lurk offshore. Any seaborne invasion must run a gauntlet of stronger and more numerous ships before making landfall, at which point all the problems of a delicate unit roster resurface.
In many ways, Harondor's situation is similar to that of Numidia in vanilla RTW. You've got sparse lands and threatening neighbors which you must face with an... idiosyncratic military. So what does a Harondorian Prince have going in his favor?
In theory, the starting position is quite defensible. Your starting realm is bounded to the north by the river Poros and to the south by the river Harnen – each of which can only be crossed at a single point. To the east loom the Mountains of Shadow, blocking any enemy advance. And to the west is the Sea. If you can train enough troops in the early years to hold those river crossings – with a reserve army in the interior in case of a disastrous breach – you may have time to grow your economy to the point where you can take the fight to the enemy. (The downside to holding river crossings is that your infantry isn't exactly bridge-defending material. Harondor's armies perform best on relatively open plains, where they can use their skirmishers to best advantage and pull off some cavalry charges against tired-out enemy troops. So when defending those crossings, it's more effective to stand your army back a tile or so from the crossing itself, and give them room to maneuver in battle.)
In reality, though, the southern border is likely the most problematic. Adunabar may border you to the north, but its nearest town, Emyn Arnen, is far away from you and close to the opening moves in any RK/Adunabar war. It's likely that your northern neighbors are going to be occupied with each other for many years before one of them decides to annex your lands.
Meanwhile, the Empire of Harad has many settlements within striking distance, and no large foe to distract it. As far as the Emperor is concerned, your Principality needs to be brought under his control, the sooner the better. All those seemingly endless armies of Haradrim that poured into Ithilien in TNS will first be funneled through your lands in DoM.
That may sound frightening – and it is – but it's better than the alternative. When fighting the Haradrim, you at least have the benefit of facing a fairly similar troop composition. If a Dunedanic faction were to invade your lands early, the heavy infantry would be unstoppable. But though the Haradrim are numerous, it is possible to defeat their lightly-armed troops with your own and use superior skirmishing and cavalry tactics to win the fight elsewhere. You'll need to know where to stand and fight, and where to hit and fade – and because of the varied nature of your troops, you'll need to do both in the same battle. The hectic nature of battles as Harondor – and the high stakes involved, since each battle lost brings the foe one step closer to wresting away one of your few towns – make your victories all the more satisfying when you pull them off.
Harondor's weakness is a kind of strength as well. Because of your status as a small faction, you are attractive diplomatically to the other powers. (In RTW, large factions become a target for the others, while small factions are viewed as less threatening.) It may even be possible to leverage this to drive a wedge between allied foes and break their alliance by first cease-firing and then allying with one of them. If nothing else, such diplomatic maneuvers can buy you some time.
Time for what? Long term, probably the best strategic option for Harondor is to push back the Empire of Harad, particularly those potentially trade-rich settlements along the coast. Harad shares a culture and alignment (Men of Darkness) with Harondor, and you can beat them in battle with a little finesse, so they make the likeliest target. Expect to get some aid from Far Harad and/or Khand, both of whom may come into early conflict with the Empire's eastern forces.
The first step in such an advance (and one that can be accomplished fairly early) should be to take the nearby isle of Tolfalas from the Haradrim. This gives you a refuge in case the mainland fight is going poorly, and can be a jumping-off point for a surprise attack against a lightly-defended Gondor, if you're feeling adventurous. Taking Tolfalas also gives Harad another target, which may lessen the pressure on your mainland armies.
Playing as Harondor, you have to be an opportunist, on the battlefield as well as in your grand strategy. You may spend years building up one of your towns, only to burn it to the ground to deny the resources to an advancing enemy. You may betray a decades-long ally whose undefended settlements provide the only means to fund your wars elsewhere. You may end up sacrificing soldiers in a doomed raid along Harad's coastline just to buy you enough time to build that crucial infrastructure upgrade. In order to survive (let alone thrive), you'll have to choose your enemies and your battles carefully, strike out unexpectedly – and pray for a little luck.