There are to be American tribes by the way I worded it. Mayans, Olmecs, and maybe even the Ice Age crossers from the Alaskan bridge Clovis and Folsom. There's also Teotihuacán which lasted from 1AD to 650AD (technically still in fair AoE time period since Yamato are from 300-800AD according to the manual), and in Peru the Chavin and Paracas.
So, the problem is that this early in time, historical records are not easy to find. Also, the lack of horses is not easy to deal with, although just maybe there may be elephants. These were ancient times, and though sometimes wooly, there were scarce pacyderms about. Just maybe... but perhaps only for Clovis.
But there's other civs that were easier to find in Africa. Axum, the Kush/Nubian empires.
Anyway, I figure I may as well go into detail about the units.
Stone Age
Clubman: These are your basic infantry unit. They are light, cheap, but provide little true power. They're available from the Stone Age, and cost 55f. Thats just a little more than a villager. They are stronger than the Club men you recall from the first AoE, and exist to counter the stone aged slinger.
Rock Thrower: Also in the Stone Age, these are the first of the Slinger line. They have a faint touch of missile resistance and a minimum range. They cost stone however so watch your back. In fact, they cost 35f/10s. Unlike RoR, these guys benefit from armor techs, which work more like in AoK here. They still use stone techs to boost power... and thensome. They are weak to melee units and strong vs archers with a bonus damage vs buildings that use stone to create.
Light Bowman: The first of the Light Archer series, the Light bowman is slightly faster than most foot units. To make them and archery ranges all together, you need a Barracks. These guys cost 45w/15g so be careful with gold. They are very bad vs slingers but are ideal for fighting clubmen.
Tool Age
Heavy Clubman: An upgrade research for the clubman. Grants slightly more hp and damage and a slight bonus vs buildings. They are still sluggishly, but they are your basic warrior and work well in this age.
Light Slinger: Upgraded from Rock Throwers, these guys get better range and pierce, but not better damage (though a bit more bonus vs archers/towers). Still good for quelling archers, they now need to be wary of cavalry.
Hunting BowMan: Upgrade of the Light Bowman, the Hunting Bowman is slightly improved with hp and damage but not range. Light Bowmen have less range than most foot archers, but are quite on par with some mounted archery units. At this point, they are very good for harassing if supported with clubs to stop slingers. Hunting bows are often small, thus they are of the light bow series. Also, light archers attack slightly faster than most other archers.
Stone-tip Spearman: If you recall a unit called 'axeman', you can discard it. The Spearman is, as you can guess, a basic cavalry repelant with a nice bonus vs cavalry which deals +50% damage vs elephant units, -25% vs chariot units, and -50% vs camelry units. They cost 35f and 25w, so be sure to chop plenty of trees. They are weak vs archers, and it should be noted not to confuse Spearmen with Hoplite unitry. They are trained at the Tool Age Barracks.
LargeBow man: The first of the heavy bow series, by sacrificing speed and attack speed for power and range, these units are actually quite adept for handling slingers, provided you can provide the gold. They cost 40w/25g, so be aware of their price before training them.
Scout Cavalry: With the coming of the stable is the basic horseman. These units are what they are, long range visioned, speedy weaklings that arent too great at combat. They cost a heap of food and are best at picking off retreating units. They cost 80f/10w. In later ages, they improve fast. Remember, you need a stable for the production of mounted Archery range units.
Scout Camelry: The counterpart of its cavalry, its also a first scout unit that sacrifices some LOS capabilities for anti-horseman power but pale vs other units as well. They cost 75f/20w. They, as well, get better in later ages. The camel bonus is -50% vs elephants and chariots. So if a camel unit does +8, it does +4 vs a chariot for example. Camels dont bonus vs themselves.
Eagle Scoutsman: Fast melee for Americans. They are like their mounted counterparts, but their payroll is more towards gold than food. They cost 30g/25f so be careful. Unlike the scout cavalry/camelry, these units have a bit of missile resistance. They can also provide the Priest countering role of chariots nicely.
Bronze Age
Maceman: From club to mace, things begin to change, including slight melee armor. Dont confuse them for the so called champs of AoK or legions in AoE, for all game, the maceman will forever exist for trash wars. Still, they are more powerful than heavy clubbers which is more than useful if you have several lying around, might as well strengthen them.
Slinger: Strengthened from the Light Slinger with more attack power and other stats, the slinger still provides good anti-archery, even vs the now likely present horse mounted bowmen. Just watch your stone.
Short Swordsman: Now, we come to our all around infantryman. The shortswordsman is what you should expect, a decent unit that grows with the upgrades it gets. In fact, short swordsmen even get some nice defenses. The problem? They cost about 40f/25g and still are weak to cavalry and archery so use carefully with backup. The Broadswordsman upgrade is available in the very same age, and has slight improvements over the unit before it.
Felt-tip Spearman: A better spearman, best gotten if your enemy relies on mounted unitry. Other than that, same old spearmen.
Axeman: Now, another new infantry introduced in the Bronze, the Axeman is anti-infantry so to speak. It deals a slight bonus vs infantry, but alsio has one vs buildings and heavy bowmen as well. Axemen have a decent attack strength but are slower than most infantry if just by a tad. They cost 50f/25w. Decent price for its lateness, the axeman must be researched however.
Short Bowman: Upgrade of the Hunting Bowman. Slight range boost comes with this age, but still same old swift bowman. Also, the Improved Short Bowman is available in this age as well.
Longbow Man: The heavy, long ranged sluggish beast. Also, Improved Longbow Man is researchable as well for another upgrading boost if your civ can learn it.
Light Horse Archer: Hit and run cavalry ranged unit. You know how it works. Its faster than most units but its range is low. They cost 45w/60g. Their price hopefully makes up for usefulness. In order to make mounted archers, YOU NEED A STABLE, or to have at least built one.
Camel Bowman: Mirror of the Horse Archer, deals less damage than the horse archer and has less missile armor, but has bonus vs cavalry units, including horse archer. They are just as fast as their cavalry counterpart. They cost 60w/50g
Light Cavalry: Upgrade of the Scout Cavalry, with more power attained. Good fun for all.
Light Camelry: Same long range vision unit as a camel. Palmyrian armies will likely find these speedy scouts useful.
Camel Rider: A heavier camel mounted unit with survivability and cavalry killing power.
Cavalry: The more war oriented cavalry unit, deals slight bonus damage vs barracks infantry and has strong attack.
Chariot: A medium power, horse mounted(well, kinda) unit that has a conversion resistance and bonus vs priests. They are a tad sluggish due to the wheeled contraptions but that adds armor. They cost 45f/60w, and will be good for trash wars later. You must research wheel at the storage pit first before you can make these.
Chariot Archer: Another archery unit, these are your charioted archery, with decent melee armor but sluggishness for a mounted unit. Again, priest destroyers. Costs 35f/75w.
Hoplite: With the Academy comes these defensive bulldozers. Heavy armor and power but so slow its ludicrous. Weak to archery units and siege, they cost a heap, 65f/50g. Make if you dare! No damage bonuses.
Light Peltast: Another Academy unit, this one is ranged, although its not truly a powerhouser, the ranged anticavalry power of a spearman is great to have. Costs 45w/10g. Weak to Slingers with their bonus.
Stone Thrower: Basic, long ranged area blasting unit. Costly and fragile, bring other units with them. Costs 110w/80g.
Ballista: The unit killing siege weapon, again, fragile, and needy of unitary defenses. Costs 95w/70g, so its less worrisome than stonethrowers.
Eagle Warrior: The upgrade for America civs scouting line. Beware, not all civs can get the fullest of their footly scouts like this.
Ill get to the iron age in a bit.
Here's a few more civ UUs.
Mayans: Mayans had a LONG spanning empire from 1000BC to 1521AD, and as such, they get their fabled Plumed Archer, a more expensive bowman that boasts missile armor and speed on par with light bowmen, just watch out for cavalry.
Nubians: A throwing spearman, faster than the Peltast, they also have greater cavalry bonus damage but less defenses. As well, they are infantry, not pierce damage. They are a poor choice vs hoplites as such.