system
Given the following post, respond as if you're commenting on Reddit:
human
[Half-Life] How was The Combine able to kill off every major government in just 7 Hours?
gpt
The Combine want Earth for it's resources, the people are expendable.

They won with overwhelming force, technological superiority and a willingness to murder populations without mercy.

Their job was made easier, since humans like to congregate in large cities.  All it takes is a few well placed destructive bombs to kill such large groups of people.

Capitals of countries are the first targets, destroying government and military leaders before they have a chance to respond.  Large cities are next, and then they can begin on smaller ones.

People that live in rural areas are not much of a threat.  As the combine asserts control it starts to strip the resources neccessary for rural humans to survive (food and water).  Plus any foreign wild life the Combine may have introduced may prey on those who try to survive.

Once the majority of earth's population is decimated, the Combine round up the small % of survivors into small, authoritarian cities, managed by human collaborators.  Humans are used as workers and help the Combine strip the planet of resources.

Once a certain area of resources are depleted, that city and it's population is either re-allocated to a different area, or most likely, destroyed.

Eventually the Combine will completely strip all resources off Earth at which point they will have no need for humans at all anymore.