Anime: Aoki Ryuusei SPT Layzner (1986)

By the year 1996 humanity has advanced enough to travel to the Moon and Mars, and establish settlements there. However, the Cold War is still going on, with ever-increasing tensions between the United States of America and the Soviet Union, and the threat of a nuclear war looms on the horizon.

But soon, an unknown menace befalls humanity: on Mars, the members of an exchange program funded by the United Nations to promote peace and dialogue between nations find themselves trapped in a crossfire between four mysterious humanoid robots - three of which begin firing on the exchange program's base, killing almost all of the students. Only a few people survive, but they find themselves isolated on an inhospitable planet that has become a battlefield. And, as if this wasn't enough, the pilot of the fourth robot, who has been trying not to involve civilians in the battle, actually presents himself to the survivors, introducing himself as Albatro Null Eiji Asuka and telling them that the Earth is being targeted for occupation by the faraway Grados Empire.

Source: TV Tropes

Note: The first two episodes, Eiji 1996 and Le Caine 1999, are recaps of episodes 01-24 and 26-38, respectively. The third episode Seal 2000 is an unaired alternative ("true") ending of the series.