Of course, the Crystal Gems and Rose Quartz believe they defeated Homeworld and forced them to leave Earth. But there have been some hints in the show that indicate that perhaps their victory was a ruse. Check out the theory below, and give your thoughts in the comments!
We’ve all accepted that Rose won the war against Homeworld. However, Greg says in The Return that Rose only managed to save ‘a few of her closest friends’. If Homeworld managed to reduce Rose’s army to so few, it seems extremely unlikely that Rose’s army could win.
In Marble Madness, Peridot describes what she’s doing as 'just picking up where we left off’, which we now know to be checking the fusion experiments and the Cluster. In addition, in Jailbreak, Peridot says to Jasper (before she is cut off) 'the whole point of coming here was to check progress on the Cluster’. It seems fairly unlikely to me that Homeworld managed to plant the Cluster and the rest of the artificial fusions between now and the end of the war, meaning the remaining option is that they had placed them there before leaving Earth. We don’t know how long a gem usually spends in the ground before emerging, but we know that the fusion experiments seen in Keeping It Together 'emerged early’.
If we connect these two occurrences, we can arrive at the following conclusion: Homeworld planted the Cluster in Earth at some point before the war ended, knowing it would probably emerge at around the current point in the show. This suggests that Homeworld decided that, instead of risking their valuable soldiers, it was better to make Rose think she had won the war but to plant the Cluster, which would emerge long after they’d abandoned Earth and would kill all life on the planet. After all, Homeworld must surely have realised that the Cluster would destroy the Earth, so it makes no sense for them to plant it while they still wanted to keep the Earth intact (at least for a while).
An alternative conclusion is that Homeworld calculated roughly when the Cluster would emerge and decided to plant it at such a point that it would emerge after they had already abandoned Earth due to its gem-growing potential having gone.
Additionally, Peridot refers to the Earth as 'abandoned crystal colony’ in Cry For Help, making it sound more like a calculated move than a forced retreat.
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