Know thy Enemy

The enemy of the series is an alien empire known as the Grex Collective, although humanity simply calls them the Grex. I wanted to give some level of uniqueness, so I didn't make them downright xenophobes. The leading species of the Grex were created by a long-dead civilization which they believed "ascended" through some form of advanced technology to another realm of existence. They hope to join their creators, but due to complicated events and dark forces at work (I will explain later) they believe they must prove themselves worthy by claiming the galaxy. Now I know that sounds like it'd involve hostilities, but they present other space farring racs two options: peacefully integrate, or be exterminated. Most species have obliged, but in the past several have tried to resist. They always failed, most of them fighting to the end and the others submitting to the Grex. Humanity refuses to integrate, and the Grex are following their pattern by launching full genocide against the human race. This fuels initial conflict. Thoughts or comments?