Homeworld was never the most friendly of places. It was made of rules and regulations and respect for authority. Even so, there were those who formed bonds with each other, who preferred the company of a certain or a few certain gems. Most just considered it to be a tactical preference- after all, some gems were better in battle together than others.
So it was that Ruby and Sapphire met, and formed a strong bond with each other. They'd fused a few times, in secret, since it was really a frowned upon act on Homeworld. It was a nice feeling, their bodies intertwining into one being, but it was always bittersweet knowing it couldn't last.
One day, the news of Rose Quartz's rebellion reached their ears. All gems were called to act, to join the war and destroy Rose Quartz and her army. She was fighting for some worthless planet somewhere out in the universe. She was interfering with the Homeworld's plans for total domination. Who cared about some living beings? Gems were more powerful, better, stronger, and ageless. The lives on this planet, this Earth, barely made it to a century old before ceasing to exists.
It was absurd that Rose Quartz thought that she was going to win, when Homeworld had a much larger army. As if the gems on Homeworld weren't enough, there were all the gems they'd been manufacturing at the Kindergarten. Yes, Rose Quartz was a fool, and so were those that chose to join her. Her efforts would surely prove futile, and those that stood with her would be crushed.