Earth

The Earth is a planet in the solar system which is featured in Plazma Burst: Forward to the Past, Plazma Burst 2 and Plazma Burst 2.5, and is the home of the Civil Security. It's population during the games' events is rougly 8 billion humans. The planet is also the original home of the Human faction on Mars, but it is unknown why they have left Earth and ditched most, if not all, communications with Earth.

Earth has seen many attempts to formally unite, but these attempts ultimately failed and lead to separation of countries and other territories. It is not mentioned in the games what countries currently exist on Earth.

Civil Security
The Civil Security are the main representatives of Earth and its technology, especially since they are Earth's army. The Civil Security has unknown goals, but judging by their name it could be seen that they are there to protect civilians in a militaristic manner.

Usurpation Forces
The Usurpation Forces are a group of aliens which belong to an unknown race, unknown planet and unknown galaxy in an unknown area of the universe. They are attacking the Earth for unknown reasons, and are shown to be much more technologically advanced than humans are.

Humans
The humans are a small faction on Mars which have settled there for unknown reasons. They have no communications with their larger counterpart back on Earth for unknown reasons.

Falkoks
The Falkoks are a peaceful faction of aliens from an unknown area which do not see any benefits from capturing Earth (gravity on Earth is different than their native planet, which affects them in unknown ways), and therefore leave it alone. Unlike the Usurpers, they are just as advanced as humans, which could also be another factor of their neutrality.