system
Given the following post, respond as if you're commenting on Reddit:
human
[Godzilla] What made the Titans...

What made the Titans go into hibernation and what made them start waking up?
gpt
I do believe it's explained in 2014 that as time passes, the average radiation levels on the Earth dropped.

With a reduced amount to feed on, many of the Titans either moved deeper into the Earth (like Godzilla), or simply went into hibernation.

Then, upon the increasingly more widespread nuclear testing and such, the surface became more 'habitable' for the Titans in the sense that they now have a more abundant source of sustenance on the surface once again.