Within no time, half of the human race was eradicated and the remaining half was waiting for its imminent death. Then the new USA emerged on the face of the world that had the alien technology to fight against its enemies and the deadliest force in the world i.e the Warp Marine Corps. With the help of this special force and alien technology, the country became able to fight against the invading aliens and it was time to pay the enemy in the same coin.
Of course, the enemy was not retreating but it finally met its match in the human world. Deadly fights on the ground and in the air are seen and the aliens too get the taste of death finally at the hands of humans who were considered weak at first.