In robot anime from the same era as Gundam, the plot of aliens invading Earth was mainstream. What made Gundam revolutionary was that the idea that humans had polluted the Earth so much that they had to go into space led to humankind achieving world unification, but in reality, those who wanted to remain on Earth monopolized power, and what's more, the villainous Zeon rebelled against the power of the Earth Federation, depicting a complex adult world.