The Day the Earth Stood Still
Released in 1951, starring Michael Rennie, Patricia Neal and Hugh Marlowe, an alien lands and tells the people of Earth that they must live peacefully or be destroyed as a danger to other planets.
Star Wars
Released in 1977, starring Mark Hamill, Harrison Ford and Carrie Fisher, Luke Skywalker joins forces with a Jedi Knight, a cocky pilot, a wookie and two droids to save the universe from the Empire’s world-destroying battle-station, while also attempting to rescue Princess Leia from the evil Darth Vader.
Source: Maurice and Nigel at thegeektwins.com