There was an alien invasion that changed everything. They killed anyone they found and took any resources they found useful. Soldiers even joined the aliens in their fight. For some reason the government sent nuclear bombs down on all of the towns. You and a group of your friends escaped the blast but you were in a car accident and you were the only survivor. The nuclear blasts combined with the alien invasion has changed Earth's atmosphere and now the air is not safe for humans and hardly any animals. You need to seek shelter that has oxygen and supplies and pick up anything useful along the way as well as other survivors. You will want their help when facing enemies.