After SKYNET leveled the world in 1997, it began a conservative, if rapid, buildup of its industrial might.  SKYNET had been careful to intercept (and thus spare) the larger facilities that had been instrumental in its own construction from the retaliation strike from Russia and the token strike from China.  Even as the radioactive fallout from the strikes was settling across the American mainland, SKYNET was already mobilizing its plans.  In 2011 AD, SKYNET consolidated its resources and manufacturing facilities in one area, a portion of the mid-Western United States which became known as Sector Zero.  Within Sector Zero, SKYNET ruled supreme and with total authority.  Huge, multi-level automated manufacturing complexes and industrial centers rose into the sky and nuzzled into the depths of the Earth.  All of the facilities were connected by a variety of cargo and unit mass transport systems, all were linked to several computer core systems, which were in turn interfaced to SKYNET directly.

SKYNET's automated mining systems began to filter out the planet's minerals, going farther and faster than any previous human attempts.  One such project became known to the humans as 'the Devil's Navel', and it was the first structurally sound deep core mine, fully automated, ten kilometers deep and increasing in depth by several hundred meters with each month.  When SKYNET found a thermal vein, it simply tapped into it and enjoyed new power for more production.  By 2018, Sector Zero was an impregnable fortress, a mechanical blemish on the surface of the Earth that could easily be seen from space, and it continued to grow every year.  By 2024, local resources had been depleted and except for the still sizeable outlay from the deep core mine, SKYNET began to expand to other areas of the country, setting up armored and armed fortresses, stationing units to both pacify the immediate area and then protect its mining interests.  SKYNET was greedy, but never wasteful.  it favored a short term, rapid depletion of immediate resources in order to exterminate the human race, followed by a protracted, perhaps centuries long, period of reclamation and recycling, a period where it would remake the Earth's surface over in its own image.

As the War raged for decades, SKYNET tried a variety of designs all with the express purpose of hunting down humans and eliminating them in any environment.  As humans became more and more organized, the need for highly specialized units became a tactical priority.  The automated factories were working at full capacity to produce units for SKYNET's arsenal while the tech and science centers processed data and developed new areas of science to utilize in constructing the next generation of killing machine.  The automated resource collection units were combing the ruins for materials to keep the vast automated factory complexes supplied, and SKYNET even had to resort to using human labor, cheap as it was, to handle some of its more simple tasks, thus freeing up machines that were used in much more valuable labor.   Labor and internment camps were constructed, and humans rounded up for labor details and after their usefulness was at an end, orderly disposal.  SKYNET soon noted that resistance to its expansion was being met with organized and aggressive resistance.  Humans were striking back, smashing forward fortifications, stealing technology, stealing weapons, salvaging destroyed units, and then fading back into the underground bunkers.  Ambushes on resource collection units became common as did attacks on and liberations of prison work camps.  Each camp liberated added to the manpower of a growing army of humans and SKYNET's response was that each prisoner be eliminated instantly if a raid was detected being conducted on a camp.  Mass executions and orderly exterminations soon taught the Resistance that it had to learn new tactics rather than brute force to liberate its fellow humans.

Sometimes, human intelligence operatives would infiltrate the prison camps and rebellion would be instigated from within.  SKYNET had its own ways to deal with infiltrators from the Resistance but the lesson was one that was not forgotten and would serve the supercomputer well in future tactics.

The Resistance learned quickly that the War was one not only of attrition, but of resources.  SKYNET's Machines, like any other army, required certain resources to be produced, to operate, and to be repaired.  If the Humans cut off the resources or took them before SKYNET could obtain them, then they delivered a blow to the supercomputer's campaign against them.   The Resistance learned that if the materials never got to SKYNET's factories, then SKYNET couldn't build its weapons. 

It was no small wonder that after the Resistance started hitting SKYNET at its resource links that HK unit production was stepped up and resource collection units soon had combat capable escorts.