The Crystal Gems are a rebel group led by Rose Quartz . They previously fought Homeworld because Rose Quartz wanted to protect the life on Earth. After the Diamonds (Yellow, Blue, and White) forced the end of the war with the corruption of all Gems on Earth (aside from the main cast of Crystal Gems, because of Rose's shield), the rebel group went into hiding, although since the birth of Steven, they have had more contact with Homeworld. (Rose gave up her physical form to make Steven, so she was never really in the show other than memories from the Crystal Gems and Greg ( Steven's dad) 