The Tears of the Sun : A Novel of the Change(Emberverse‪)‬

It's Change Year 25, a generation after high-energy technology died in a catastrophe most of the human race didn't survive.
The children born after the Change are now starting to take center stage-and Whoever or Whatever was behind the Change itself may be taking a hand in their rivalries. An expedition has travelled to Nantucked across a strange and hostile continent to find some answers.