system
Given the following post, respond as if you're commenting on Reddit:
human
[Half Life 2] Possible Spoilers: Combine Question

Why didn't the Combine just kill all the humans after they entered our world. I mean, they seem to be open to killing and even causing the extinction of our species using the suppression field. They clearly are intent on occupying Earth in the foreseeable future so why keep humans alive?
gpt
If there is an infinite number of dimensions then it doesn't matter how big the Combine forces are they will never be big enough to conquer them all. But they could defeat the native species and have them rule themselves under the Combine banner. 

Similar to how the British Empire conquered other countries. Why should Brits occupy India when they could simply build a British Indian Army and had them rule themselves in the name of Britain.