Mars

Mars is the planet that houses the largest human population outside of the Homeworld of Mankind and that is believed to be the only planet in the Solar System aside from Earth that's classified as a Terran Planet. It was fully terraformed in the aftermath of the Blackout and its population is steadily climbing ever since, projected to reach two billions by the end of the 23rd Century. This growth is limited only by the reproductive capabilities of the planet's inhabitants.
Eventually, though, Venus is projected to outgrow Mars thanks to its heavier gravity and larger surface area.
The other thing that the planet is notable for is the fact that it's in a state of de facto civil war, caused by the political split between pre-terraforming settlers and the later immigrants. While no battles are waged, the planet has two governments that do not recognize each other as legal representatives of the people of Mars. As a result of this strife, the Solar Commonwealth stepped in and maintains control over the orbital installations and the Martian fleet in order to prevent both sides from trying to establish an orbital blockade which would definitely start a war.
All while trying to act as the mediator. Thus far, unsuccessfully.

Geography

Three large bodies of water - an ocean to the north (reaching the pole and, hence, having rather cool water) and two endorheic seas near the equator, connected to the former through some rivers and canals. The hydrosphere also includes a lot of lakes and rivers, typically taking advantage of what's left of the canals on the Mars surface (as a result, they requires next to no human intervention to form).
There is one large continent. Its north is mostly pleasant to live and composed of temperate plains resting upon the edge of the ocean, while the south is mountains and extremely arid (except the areas surrounding the Argyre and Hellas seas. While the closest thing to Second Earth that the Solar System has, it's far from perfect, with especially the regions closer to the poles being downright inhospitable, with a temperature changing from 15C during the summer solstice to -70 during the winter solstice.

Climate

Due to the axial tilt, expect hot summers and cold winters, to the point where it qualifies as a 'harsh climate' for most. Even its temperate zone is closer in climate to southern Siberia than Europe.

Fauna & Flora

Varied, but still rather limited. This is caused by the fact that while the Sidhe terraformation technology could, indeed, turn atmosphere breathable and - with the help from some redirected comets - quickly create and stabilize the hydrosphere, there were things that it couldn't do. For example, while they can turn the rocky surface into a soil, their ability to create organic matter is extremely limited.
As a result, soil is there but it's nearly barren. Just as the Earth's main objective is currently restoration of its climate and ecosystem, the main objective of the population of Mars' the soil on the planetary scale, importing immense amount of fertilizers (natural and not, for as long as the latter doesn't risk long-term damage to the soil) and spreading it throughout their world. With every year, Mars grows more and more fertile, allowing Martians to introduce new species to their planet.
Today, there are forests on Mars. Few and far between, but they're steadily expanding and so does the diversity of animals and plants living in them. Freshwater oceans of Mars are also growing more and more populated, having the second most vibrant ecosystem within the Solar System.

Natural Resources

Mars possesses a lot of natural resources, especially iron. In a way, it is like Earth, except that its resources weren't depleted by millenia of exploitation. Add a lot of rivers that can serve as a source of cheap energy, and you end up with Mars being anotable industrial powerhouse within the Solar System, and one that seems to be the least dependent on asteroid mining to maintain its production output.
Due to the lack of organic materials (like wood and leather), its products tend to go for more 'utilitarian' aesthetic, with metals being the dominant material even in making furniture.

History

Mars is counted among the oldest human colonies, with only Luna being older. It has remained the bastion of the Alliance for the Preservation of Democracy between the Third and Fourth World War, only to become de facto independent after its collapse, although maintaining at least some ties with the former APD countries.
The situation changed following the Blackout, when the planet was rapidly terraformed and began to be flooded with immigrants leaving Earth in the aftermath of the Fourth World War. This caused a rising conflict between the descendants of those who called the planet home for decades despite having to live in closed arcologies and those that came in only when the planet was made habitable, which spiralled into the current crisis.
Today, the two main governments on Mars are located in the Arabian Gulf and the Elysian Peninsula. The latter is controled by the Old Martians while the former by the New Martians. The rest of the planet resembles a patchwork, with some local provinces refusing demands from both sides and instead considering themselves neutral in the on-going struggle.

Mars
Summary
Distance from Sun: 150.000 mil. km
Diameter: 4000 km
Solar Constant: 0.8
Mass: 0.09 Earths
Gravity: 0.376g
Mean Density: 3 kg/l
Orbital period: 800 Earth days
Day length: 20 h 37 m
Rotation Axial Tilt: 15 degrees

Astrography

Object Type: Terrestrial Planet
Object Subtype: Terran
Primary Location: Core Sector
Secondary Location: Solar System
Tertiary Location: Mars Subsystem
Satellites: Deimos & Phobos
Transshipment Station: Deimos

Habitation Status

Status: Colonized
Classification: Civilized World
Population: ~324 mln.
Capital: Disputed.
Government: Multiple, Listed Beneath
Solar Commonwealth Member: Yes.

Governments
Elysian Government
Arabian Government