"Crusade" is a short story

Short story

A short story is a work of fiction that is usually written in prose, often in narrative format. This format tends to be more pointed than longer works of fiction, such as novellas and novels. Short story definitions based on length differ somewhat, even among professional writers, in part because...

 by Arthur C. Clarke

Arthur C. Clarke

Sir Arthur Charles Clarke, CBE, FRAS was a British science fiction author, inventor, and futurist, famous for his short stories and novels, among them 2001: A Space Odyssey, and as a host and commentator in the British television series Mysterious World. For many years, Robert A. Heinlein,...

 published in 1968 and republished in The Wind from the Sun

The Wind from the Sun

The Wind from the Sun is a 1972 collection of short stories by science fiction writer Arthur C. Clarke. Some of the stories originally appeared in a number of different publications...

 as well as The Collected Stories of Arthur C. Clarke

The Collected Stories of Arthur C. Clarke

The Collected Stories of Arthur C. Clarke, , first published in 2001, is a collection of almost every science fiction story shorter than novel length that Arthur C. Clarke has ever published: with 114 in all arranged in order of publication, "Travel by Wire!" in 1937 through to "Improving the...

.
It follows the extremely long life span of a natural artificial intelligence that exists on a freezing planet in the vast space between two galaxies. The intelligence sends out scouts into another galaxy

Milky Way

The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 to seek other life like themselves, only to discover the inhabitants of planet Earth, whose physique is very different from their own. Tens of thousands of years pass to collect data about the humans, before the intelligence decides to send a "crusade" that will reach planet Earth in the year 2050.