A new book by veteran journalist Chhay Sophal, released on Saturday, argues that politicians on both sides on the political divide should discuss a concerted strategy to “claim back” territory from Vietnam that was once part of a Khmer kingdom.

The book is likely to be controversial, coming amid heightened tensions between the two countries and political forces in Cambodia that led to protests and clashes earlier this year.

Over the past three years, Sophal, a former Reuters reporter and journalism lecturer, has collected official documents, conducted interviews and scoured media reports to compile this work, a 400-page tome titled Friend Enemy: Cambodian-Vietnamese Maps and Territory (1623-2015).

The book focuses on recent developments, particularly the roles of Prime Minister Hun Sen and opposition leader Sam Rainsy, weaving in elements of regional history the author says has largely been forgotten to make way for the realpolitik of the present.

“I think both actors have played important roles. They have so far argued in their own interests on the matter, but the [ruling party] had hidden and kept secret documents while claiming to protect the nation,” Sophal said.

“Since the release of the documents, the tension has subsided,” he added, referring to recently released maps.

The book is the second written by Sophal in as many years. Last August he published Cambodia’s 36 Prime Ministers, while in 2012 he wrote a 350-page study of Hun Sen post-1970, described at the time by Information Minister Khieu Kanharith as an “admirable achievement”.

Sophal said Friend Enemy also detailed how international diplomacy had been shaped by the disputes over the demarcation of the Cambodia-Vietnam border, which he argues should have been included in school curricula.

“I think it will be difficult to advocate for or demand the territory be returned. But I hope this book raises politicians’ awareness to figure out how to claim the land back.”