"Doom 3 is essentially a remake of the original games. So it doesn't take place after the events of either Doom or Doom 2. The story takes place in the year 2145. Most of Earth's natural resources have now been used up so we need to start looking to colonize another planet. Obviously the first choice of a new planet is Mars. A former military organization called Union Aerospace Corporation has many outposts on Mars consisting of scientists, corporate individuals, and plenty of marines. Their goal is to develop machinery that can instantly turn the vast deserts of Mars into water, air, and green grass providing people with a new place that they can call home. The research is going along perfectly and most of the machinery has been developed and is being tested. However, some other experiments are going on behind the scenes."