EDGE has a write-up on the making of the original X-COM title, X-COM: UFO Defense, also known as UFO: Enemy Unknown, which includes a few snippets from developer Julian Gollop, who's currently busy working on his Chaos remake. Here's a snip:
(When we first got the contract with MicroProse we were very pleased but concerned about what they might require us to do,) he says. (We did have a few arguments in the beginning because they didn't understand the game design I had written. They couldn't see how the game was going to work. I had a tough job trying to explain it, and I had to produce a few more documents and attend a big meeting with their in-house designers, producers and head of development,) said Gollop.
The original demo was for a relatively modest, two player tactical game. MicroProse asked them to base the action on Earth and to expand on the original design to deliver something more in keeping with the other epic strategy games it already had on its roster. (That prompted me to add the strategic level, with the basic idea of an alien infiltration of earth and the need to capture and research the alien technology to defeat them. It was quite a radical design in many respects, but we were trying to create a grand scale that would rival that of Civilization. In fact the research and technology tree somewhat emulates the role of advances in Civilization, but it also helped to develop the storyline.)
Inspiration for the organisation carrying out these activities came from SHADO in Gerry Anderson's UFO TV series, and also from Timothy Good's book Alien Liaison. (After reading that I knew I was on to something good. The whole alien conspiracy angle was quite exciting, and the mind control powers of the aliens he described were chilling,)?said Gollop. (The book explained some of the alleged attempts by the US government to capture and replicate the alien technology, and even make some kind of secret deals with the aliens. All this would find its way into the game in some way.)