Almost everyone comes to Cambodian history through the Khmer Rouge, which means they meet the country at its worst moment and work outward from there. That order distorts everything. Angkor was the largest pre-industrial urban complex in the world; the French protectorate lasted ninety years; Sihanouk maneuvered through the Cold War for two decades before the coup that opened the door. Reading forward puts 1975 in a story rather than making it the whole story.
There is a second reason to sequence properly. Khmer Rouge ideology drew explicitly on Angkorian imagery — the irrigation works, the mass labor, the vision of a self-sufficient agrarian empire. You cannot see what they were invoking if you have not read about what they were invoking.
Start with the survey and the ancient state
A history of Cambodia by David Chandler is the standard one-volume history and the correct first book. Chandler covers the whole span from prehistory to the contemporary period, and he is consistently careful about the limits of the sources for the earlier centuries.
Angkor and the Khmer Civilization by Michael Coe is the archaeological account — temple building, water management, kingship, and the Hindu-Buddhist religious system that organized it. Charles Higham's The civilization of Angkor covers similar territory with more emphasis on the pre-Angkorian polities and the excavation evidence. The two overlap considerably; if you want only one, Coe is the more accessible entry and Higham the more archaeologically detailed.
Then the colonial and independence periods
The French presence in Cochinchina and Cambodia by Milton Osborne is the scholarly study of how the protectorate was established and administered, and of what nineteenth-century French rule actually changed on the ground. It is dry in places and it is where the modern Cambodian state gets its administrative shape.
Osborne's Sihanouk follows the king-turned-prince-turned-politician who dominated Cambodian public life for half a century. Osborne knew him personally and the portrait is neither hagiography nor hatchet job — essential for understanding the neutrality policy, its collapse, and the 1970 Lon Nol coup.
Then the revolution
Brother enemy by Nayan Chanda is the reporting on the wars after the war: the Khmer Rouge–Vietnamese conflict, the Chinese-Vietnamese clash of 1979, and the diplomacy that kept Democratic Kampuchea in its UN seat for years after its atrocities were known. It is the book that explains the international politics almost every other account skips.
The Pol Pot Regime by Ben Kiernan is the most detailed scholarly treatment of the years 1975–79, built on extensive interviews and document work. Kiernan's estimates and some of his earlier positions have been debated, and it is worth knowing that; the book remains the standard reference for the regime's structure and its death toll. Elizabeth Becker's When the war was over is the more readable narrative of the same period from a journalist who reported it at the time.
Close with witness and aftermath
First They Killed My Father by Loung Ung is the survivor memoir that keeps all of the above from staying abstract — the evacuation and the labor camps through a child's eyes. Finish with Cambodia's curse by Joel Brinkley on the decades since: the UN transition, the tribunal, the aid economy, and the durability of Hun Sen's rule.
Follow the full path to keep the order, or browse /discover for the surrounding Southeast Asian reading.
Follow the full ordered path here: How to Learn Cambodian History from Books, in Order.
