McQuarrie was given an impossible task, to fully visualize the future of Science Fiction. Lucky for him, George Lucas, founder of Lucasfilm had a very specific idea for what that would be. Flash Gordon but not as shiny and new looking, this is war and both sides are struggling for resources. Everything needed to move fast because George likes fast cars and the vehicle design needed to match that. Every planet is one biome so make the environments as interesting as they can with that in mind.
Lucas' conditions served as guidance for McQuarrie to explore the vast galaxy. This in turn influenced stage sets, props, casting, story telling, and pretty much every aspect of the developement process.
