system
Given the following post, respond as if you're commenting on Reddit:
human
[war of the worlds] if the Martians studied planet earth for a million years before launching their invasion, why didn't they know about germs? And why didn't they attack before humanity had built defensive capability?
gpt
- Interplanetary war is hard, you put it off for as long as possible.  The Martians were waiting until the moment when humanity could possibly pose a threat to them, 

- Humans have advanced more in the last hundred years more than they had in the previous hundred thousand years.  That exponential growth took them off guard.  Also, while humanity didn't pose all *that* much of a threat to the Martians.  If it weren't for the germs, we'd still have been soundly stomped.
  
- Something in the way life evolved on mars meant micro-organisms weren't an issue at all.  It's hard to look for something like that when you don't even know it could be a problem.