In the early second millennium of the Third Age, the Witch King took over the fortress of Carn Dum and founded the realm of Angmar. He ruled there and waged war upon the Dunedain, until his defeat in TA 1975.
When I first read The Fellowship of the Ring, I thought it odd how sparsely inhabited the lands seemed. Just the Elves and Dwarves to the West, then the Shire, then Bree and eventually Rivendell. Now that I've read a bit more, I know that that these lands were inhabited afterall, and where they weren't, there was good reason.
At the end of the first Age, the faithful Edain (men) were rewarded with the Island realm of Numenor. However, men still remained everywhere in Middle Earth. When Numenoreans returned in the Second Age, they re-made contact with these peoples, 'civilising' some, and conquering others, and driving away many more. The great Kingdoms the faithful Numenoreans founded after the fall, Arnor in the north and Gondor in the South, were surrounded by displaced peoples, who would not give fealty to the invaders.
This was ready material for any evil lord, bent of destroying the heirs of Elendil. Just as Saruman was to do at the end of the Third Age, so did Sauron's chief servant do in the cold lands at the north of the Misty Mountains.
Carn Dum means 'red valley' and the backbone of the Witch King's forces, year in, year out, was provided by the hillmen who lived in that region.
Though the Witchking was a dread master, the warrior elite of those peoples were lured by the promise of wealth, fear of the Witch King's retribution, and the prospect of vengeance against the lowland invaders.
Those that actually fought were the select warrior strata of those societies. Orcs aplenty were available as simple fodder, and bred quickly. The warriors of Carn Dum provided the skilled core of Angmar's warhosts. They lacked the drilled formation and maneuver of the Dunedain forces. However, they made up for this in the fury of the charge, seeking to smash the enemy ranks in coordinated assaults, then defeat them, man to man, in brutal melee.
While these men fought, their lands remained safe, even prospered, free of the attentions of the evil creatures drawn to the Witch King's power. These creatures: orcs, shades, wights, trolls and wargs, were instead directed toward the ruin of the Dunedain. So for hundreds of years, beneath the cold shadows of the Red Valley, the men women and children of the hillmen lived out their lived tending their crops, herding their livestock and making their homes.
In order to match the armies of the Dunedain, their warriors were kitted in mail and armed by the foundries of Angmar. Their equipment compares well to the best enjoyed by the men of this time, equaling that worn by the warriors who fought in the battles of 'The Last Alliance' against Sauron. In WOTR terms, this is a defense of 4(6) when equiped with a shield. The best warriors of Arnor outdo them, with a defense of 5(7), but the warriors of Carn Dum are better equiped than most men of their time, who would wear only limited mail and perhaps a shield, a defense of 3(5).
Their principle strengths are their stout shield wall and the measured aggression of their charges. When they charge, they benefit from the 'Berserk' special rule. On a roll of a '1' they will expose themselves to additional casualties, unless they have a chieftain on hand to ensure the charge is carried through. Otherwise, they hit hard, str 5 on a 2-5 and a fearsome str 7 on a 6. These men can shatter the any formation.