The Mysterians (1957)

Aliens and other science fiction/space opera elements are commonplace in Godzilla movies by today's standards.  In the 1970s, nearly every film rounding out the original Showa Godzilla series featured an alien invasion as the main conflict for increasingly cliched plot.  However, that wasn't always the case.  In the late 1950s and early 1960s, Toho and Ishiro Honda cranked out several alien invasion epics that stood as unique twists on a classic plot, bolstered by Eiji Tsyburaya's magnificent effects work.  The first outing into alien territory came in 1957's The Mysterians.

Astronomers and Astrophysicists have discovered a new asteroid, along with an interesting theory that the floating space debris was originally part of an undiscovered planet located between Mars and Jupiter.  The debris is named the Mysteroid, though most of Earth's scientists laugh off the theory as being somewhat fantastical.  Furthermore, Shirashi, the man who came up with the theory, has gone missing following several fires and earthquakes that have wiped out his hometown.

Soon after, the cause of the earthquakes is discovered to be Moguera, an enormous robotic mech specialized at digging and burrowing.  Moguera is something of a fan favorite in the Godzilla fandom, perhaps more well known for its later appearance in the Heisei series in Godzilla vs. Space Godzilla.  In fact, the whole idea of adding the giant robot came as something of an afterthought quite late in the film's production.  Still, the hulking mech is one of (if not the) the film's most iconic additions, and is a delight to watch on screen.  Moguera's rampage continues, and the JSDF is called in to destroy it.  However, preliminary attacks show that the mech's metallic hull is impervious to conventional weaponry.  As the enormous robot tries to cross a bridge in order to level a nearby town, the bridge is detonated as a last resort, causing the robot to tumble into the river below, short circuiting and exploding. At the Diet Building, Atsumi briefs officials on what has been learned about the Moguera automaton. The remains of the giant machine reveal that it was manufactured out of an unknown chemical compound. 

Shortly afterwards, astronomers witness activity in outer space around the moon. They alert the world to this discovery, and not long after the aliens emerge, as a gigantic technological dome erupts through the Earth's crust near Mount Fuji. A group of scientists are politely ushered into the dome, where the Mysterians, a scientifically advanced alien race, list their demands from the people of Earth: a two-mile radius strip of land and the right to marry women on Earth. The reason for this is that 100,000 years ago their planet Mysteriod, the once fifth planet from the sun, was destroyed by a nuclear war. Fortunately, some Mysterians were able to escape to Mars before their planet was rendered uninhabitable. However, due to the nuclear war, Stronium-90 has left 80 percent of the aliens' population either entirely sterile, deformed, or crippled. The proposed interbreeding with women on Earth would produce healthier offspring and keep their race alive. The latter part of their demands is downplayed as they admit to already taking three women captive and reveal two others that they are interested in.

Appauled at the arrogance of the Mysterians, Earth refuses their demands and begins the mobilization of its armed forces around Mount Fuji. It's also discovered that the missing scientist whose theory about the Mysteroid was correct has resurfaced, and revealed to have sided with the aliens due to their technological achievements.  Furious at Earth's opposition to their plight, the Mysterians increase their demands, asking for a 75-mile radius of land, as the Earth continues to develop a new method of attack. Earth's efforts in this matter pay off as the Markalite Flying Atomic Heat Projector, a gigantic lens that can reflect the Mysterians’ weaponry, is developed and put into action against the alien base. 

Ultimately, a twofold final attack on the Mysterian base is enacted, as the abducted women are rescued, and Shirashi - who had previously sided with them - turns on the aliens and sabotages their defenses from the inside, while the forces of Earth attack from the outside.  Finally, the Mysterian base is destroyed, and Earth has been saved from the extra terrestrial attack... for now.

While the premise of alien invaders abducting Earth's women and holding the planet hostage isn't anything new, The Mysterians does a valiant effort at trying to give this premise the most cutting edge effects and visuals of the time.  While it's not overtly impressive by today's standards - beyond the Moguera sequences, and perhaps the Mysterians' brazen and colorful appearance - this is a tactic that has been tried many times throughout cinematic history to great success.  For what is Independence Day if not a remake of Earth vs. the Flying Saucers with newer effects and a bigger budget?