A MacGuffin is a term for a motivating element in a story that is used to drive the plot. It serves no further purpose. It won't pop up again later, it won't explain the ending, it won't do anything except possibly distract you while you try to figure out its significance. In some cases, it won't even be shown. It is usually a mysterious package/artifact/super-weapon that everyone in the story is chasing.
I have an idea for a story in a space opera setting where multiple empires fight over who controls a planet.
- There are multiple space-faring empires, each one controlling a couple star systems.
- Someone discovers a new habitable planet (must be habitable because I want colonists to settle on it).
- There is something awesome about that planet which makes all the empires want to control it.
- The empires can't or don't want to share, even with their closest allies.
- Those who have no chance to control it want to destroy it or at least make it uninhabitable to deny it to their enemies.
- That something awesome about the planet doesn't provide an advantage which makes it notably easier to defend the planet against the other empires, nor does denying it to the other empires stop them from being a threat. Still everyone wants it.
In other words, the planet is a MacGuffin. Everyone wants it, but the reason why they want it has not much effect on the plot.
What could that something awesome be?