Hi Liz,
The word 'amidst' is a preposition. In this context, it can be understood as meaning 'in the middle of' or 'during'.
An easier way of thinking about this sentence would be:
War burns memories of pain into the minds of those who survive and attempt to return to normal life while the nation rebuilds itself.
Another example using the same word:
There was one black bird amidst a flock of white pigeons.
I hope this helps!