"War?!", thought Greg shockingly after hearing what the man said.
He thought back to the moment when he was back in that gigantic tree palace with Joe. He clearly remembered what that creature, which called himself Kragnas, said to him before with a creepy smile while his whole body got frozen into an ice sculpture.
"Brat, listen carefully. Maybe you won this time, but don't think even for a second that we are finished like this. When the time comes, humans will taste what real despair is, and as for you..."
Every word that the creature said to him before he was pushed out of the zone was clearly inside his head. At that time he didn't understand it, but now after hearing the word 'war' insanely knew that there will be truly a huge calamity.
Or you can't even call it war, because with the current level of the humans it wouldn't be exaggerated to say it will be a total massacre.