system
Given the following post, respond as if you're commenting on Reddit:
human
[Terminator] How did the resistance win the war against Skynet?

The resistance against skynet seems to be incredibly outclassed in nearly every engagement, and even when the resistance does win battles they usually sacrifice valuable personnel and equipment to do so. How could the resistance ever win in a drawn out war against the machines?
gpt
Reese tells Sarah Connor that Skynet's "defense grid was smashed" and that the Resistance had already won when it decided to send the first Terminator back in time. 

The implication was that they took it down with brute force, probably throwing everything they had at the *literal* defensive fortifications surrounding the Skynet mainframe. This was only possible because John Connor started liberating concentration camps, allowing the Resistance to build up an army of humans significant enough to eventually overwhelm Skynet's defenses. (That's why Connor was so important. If it was just some kind of virus or computer attack that allowed the Resistance to win, Connor wouldn't have been as crucial.)

If you want to take it further, it's likely that Skynet didn't actually have a very large army of Terminators, HKs, and other equipment before John Connor started ruining their shit. Why would they need it, when all they were doing was cleaning up a weakened, radiation poisoned population of survivors? Skynet probably didn't *predict* there to be a Resistance at all, and so it was taken by surprise.