The book is written by David P. Chandler, an American historian who came to Cambodia in 1960 as a US officer. He is recognized as one of the foremost western scholars of Cambodia modern history.
The book will give you a brief history from the Angkor period to the present. It has been revised for 4th edition in 2007.
If we want to have an update on the current situation, some information might be out of date. But at least the book will give you a good understanding of Khmer history from the past up to its revised date.
The author divides the book into different parts according to the timeline which you can skip if you are not interested in any period.