In the distant future, Earth is ruled by a militaristic regime known as the Global Federation of Earth, which took power after the Galactic War Veterans overthrew democracy. This regime encourages citizens to join the Mobile Infantry, promising them citizenship in exchange for military service. Only citizens enjoy rights such as voting and procreation, while ordinary civilians are denied these privileges.

Humanity is in a tense conflict with a race of highly evolved insectoid creatures called the Arachnids, or Bugs. One of their planets, Klendathu, is launching meteorites toward Earth, prompting the military to plan an assault to eliminate Klendathu and protect humanity from the impending threat.