Rod Serling turned this short story by
Damon Knight into one of the
best episodes from Serling's television series
The Twilight Zone. First aired on March 2,
1962.
The alien
Kanamits arrive on Earth and start solving all the world's problems. A few warmongering generals are skeptical, but the Kanamits are here only to serve man, which they prove by giving the United Nations a copy of a book which guides them in this principle (of course it's in the Kanamits' own language).
The world disbands its armies, and the Kanamits build domes around Earth's cities. An unlimited food supply, and free energy.
They then begin offering free passage to their home world... thousands sign up, including the main character, government codebreaker
Michael Chambers.
Rather than spoil the rest of the story, I suggest you find a tape of the episode, or wait until it's shown on TV again.