Don't leave us hanging! Please mention the book's name and author so others like myself can mean to read it too.
I'm just half joking, I suffer from a large historical blindspot for that part of the world and I'm trying to collect a list of books to read over the next two years to address this perceived (by myself only) issue.
Its by Augustus F. Lindley and called Ti-ping tien-kwoh; the history of the Ti-ping revolution Volume I and II. And its actually 955 pages. Its an account written by one of the generals fighting for the rebels, who was also a British guy. Its part history part memoir. Kind of a weird book.
I suspect those other books people mentioned are probably better if you want a good understanding of the war that's not one sided and written in 1866. But its one of the very few contemporally written first-person works available.
Edit: you can find it on Project Gutenburg for free if you want to take a look at it. https://www.gutenberg.org/files/39180/39180-h/39180-h.htm
These are not 1000 page books (but combined they can be):
- God's Chinese Son: The Taiping Heavenly Kingdom of Hong Xiuquan (more about the Taiping and their leader)
- Autumn in the Heavenly Kingdom: China, the West, and the Epic Story of the Taiping Civil War (more about the west's actions)
I just saw this book on Amazon and haven't read so might be a good read to round out the history: Struggle for Empire: The Battles of General Zuo Zongtang (Qing statesman and army officer, General Tso's chicken was named after him!)
Overall, I would say good English material on this conflict is a bit thin. I would recommend reading more about the Qing dynasty, Opium wars, first Sino Japanese war, Boxer Rebellion, Xinhai Revolution. /r/askhistorians always have good books recommendation.