In general, most of the game takes place on a world called Terra Nova, a former colony of Earth, and at its most basic there are two major polar powers, the Confederated Norther City States and the Allied Southern Territories.

The CNCS is composed of the Western Frontier Protectorate (military/clan based society with a strong old west vibe), the Northern Lights Confederacy (basically a modern western democracy but with a strong conservative religious streak), and the United Mercantile Federation (a Corporatist state where government is funded and voting rights allocated by purchasing electoral vouchers). Each League has its own military, but also contributes to the shared Northern Guard which is generally the most capable fighting force in the North and absorbs the others in times of major war. The NG tends towards specialized purpose-built units and its units tend to have more squared/box looks.

The AST is dominated by the Southern Republic (a fascist/imperialist state that strongly values personal freedom and individuality so long as one toes the state line), it also includes the Eastern Sun Emirates (ostensibly run by descendants of officers of a crashed spaceship, the Eastern Sun, as independent Emirs under a Patriarch, but largely is a puppet vassal state of the SR, who turned the Emirs into corrupt hedonists ruling over dirt-poor masses), the Mekong Dominion (southern counterpart to the UMF, but with an east-asian flavor), and the Humanist Alliance (a scientifically constructed collectivist society forced into the AST by the Southern Republic, lots of 1984/Brave New World vibes but nowhere near as bleakly dystopian, largely the most technologically advanced League on the planet). Like the CNCS, each league has its own military (in the Emirates case, each Emir has their own forces), but also contributes to the shared MILICIA. However, the Southern Republican Army is by far the largest and most powerful military force in the South, with the MILICIA being a supporting arm where disgraced SRA units/personnel or conscripts from other leagues are sent and are used for crappy/boring/dangerous/"dirty" work. Southern units tend to be more generalized in capabilities and have more rounded/curved looks.

Peace River is an independent corporate state and significant arms producer located in the badlands between the two polar powers. Tends to have even more generalist units than the South, with the idea that they often operate far from support and kinda have to do everything on their own, for instance where the Polar advanced strike gears like Jaguars and Black Mambas prioritize raw performance, the Peace River Warrior IV trades some agility for ECM capabilities and extended range sensors where a Polar force would have specialist units for that.

There's also NuCoal (New Coalition) that's composed of various badlands city states and remnants of the first CEF invasion, which has also since incorporated much of the Humanist Alliance after the SR actively attempted to annex the HA instead of just dominate it. NuCoal tends towards speed and hover units, with a strong Southern influence on designs.

The CEF is the Colonial Expeditionary Force, the military forces of a resurgent fascist Earth looking to reclaim its lost colonies (hundreds of years after abandoning them following a populist/nativist political party coming to power and ending subsidization of the "taker" colonies, and mothballing most ships capable of interstellar travel,, then blasting itself to pieces in a third world war for a couple hundred years), with a greater emphasis on (hover)tanks, energy & guided weapons, and super soldier infantry than on mechs/robots (though they do have some of their own).

There's the Black Talons, a force composed from all Terra Novan factions that are the elite of the elite formed to take the fight to the CEF. Top of the line equipment, veteran pilots, stealth ability, tons of maneuverability and rerolls, but with a small unit count.

Caprice is another colony world, largely run by a conglomeration of various megacorporations, with most of the planet living in a giant canyon trench with hundreds of milions of people in a giant megacity, that was reconquered by Earth and has been forced into collaboration as the staging point for Earth to retake its other former colonies and often has its forces conscripted to fight alongside the CEF. Their forces are composed of quadruped walkers that tends more towards slightly bigger/more powerful units than average Terra Novan units, but not radically so, though pretty much all their units are also excellent climbers.

Utopia is much the same as Caprice, but much more willing in its collaboration with the CEF and is built heavily around Drones and advanced technology. There's also Eden but they're not terribly well fleshed out.

One can also make a Badlands force made from the low to upper-mid-tier units of most of the other factions.