'within four chapters of the end'

Hi.
I have a question. Before my asking, I will give you a long quotation. Would you please read and help me understand that?

***Quotation;
Before departing, he visited the newly conquered Boer capital and interviewed Lord Roberts and other officers for his book, of which he had already penned a substantial amount. Writing to his mother, he informed her, 'I have my history (the book about the Boer War) done within four chapters of the end, unless the end of the war is unduly prolonged. I may hope to have it nearly done before I reach England.'***(the end of the quotation)

My question is about "within four chapters of the end".
In my understanding, he was writing his book not from the beginning of the war but the ending.
And what does 'it' of "I may hope to have it nearly done before I reach England" mean? His history or four chapters of the end?

Thank you.

[Red5]

He wrote his book from the beginning. He was suggesting that the war was nearly over, and therefore he could see himself writing no more than three more chapters before completing his book.