Background of the game:
The year is 2374 A.D.
The "Terrans" have been mining the Jovian System (around Jupiter) for 110 years. The spacecraft use water as fuel (fusion drive) and since Europa (one of Jupiter's moons) has large amounts of water-ice, it was one of the first to be colonized.
These colonies hold well over 200,000 people.
Well, the mining reached the rocky core of Europa. They found a hollow portion within the core and drilled through to find they had awakened a long-sleeping race of aliens.
Obviously upset, the aliens reacted angrily--killing the miners in the core and by using a powerful weapon to blow through the interior of the moon, they destroyed the colony's capital, Europa City in the process.
The Terrans are not only faced with human's first extraterrestrial contact, but also their first extraterrestrial war. One big problem: Europa is not a military colony...therefore there are few weapons or specialized military vehicles.
The colonists had to be resourceful by adding extra side plating, guts, and other parts from existing mining devices to prepare for the onslaught.
Since one person is rarely critical in all places, you move from character to character as they become pivotal in the storyline.