In Star Wars fanfic, a slave army might be the result of the Empire's cruel practices. They could be using enslaved individuals as cannon fodder. This can lead to stories of rebellion within the ranks of the slave army. Some might rise up against their oppressors, inspired by the Rebel Alliance's fight for freedom.
A slave army in Star Wars fanfic can be a really interesting concept. It could be made up of various species that have been forced into servitude. For example, the Hutts are known for having slaves, and a fanfic might explore an army of slaves they've assembled to fight their battles. It adds a new layer of complexity and moral exploration to the Star Wars universe.