Loved the premise and the concept of the book! The first half was at a nice pace and you can see the events roll smoothly even though they are told in the form of letters exchanged between the main characters. English is my third language so when the amount of letters that fell increased I found it a bit harder to understand what's going out and I was just struggling to read the words but tbh that's expected and I knew that would happen eventually. 
Personally, this entire book felt like a collection of acts of resistance that you will see happen to the opressed, even nowadays, and how they deal with it such as:

I'm ranting at this point but this book feels like a watered down version of what's is going on in a lot of countries like Palestine, Sudan, democratic republic of Congo... too many countries unfortunately.