1. The soundtrack includes a theremin
    The Day the Earth Stood Still, The Thing
  2. There's a not-so-subtle communism metaphor
    See Invasion of the Body Snatchers
  3. The world is battling an outer space invasion
    The War of the Worlds, etc
  4. A giant something or other is attacking the citizens of some poor city
    See Godzilla or Attack of the 50-Foot Woman, Them.
  5. It bears repeating: space invasion.
    Invaders from Mars, It Came from Outer Space.
  6. "It Came" from somewhere
    See It Came from Outer Space, It Came From Beneath the Sea, From Hell It Came
  7. John Agar is the star
    See The Mole People, Attack of the Puppet People, Revenge of the Creature