History may be written by the victors, as Winston Churchill is said to have observed, but the opening up of archives can threaten a nation every bit as much as the unearthing of mass graves.

That danger explains a decision quietly taken last month by Benjamin Netanyahu, the Israeli prime minister, to extend by an additional 20 years the country’s 50-year rule for the release of sensitive documents.

The new 70-year disclosure rule is the government’s response to Israeli journalists who have been seeking through Israel’s courts to gain access to documents that should already be declassified, especially those concerning the 1948 war, which established Israel, and the 1956 Suez crisis.

The state’s chief archivist says many of the documents “are not fit for public viewing” and raise doubts about Israel’s “adherence to international law”, while the government warns that greater transparency will “damage foreign relations”.

Quite what such phrases mean was illustrated by the findings of a recent investigation by an Israeli newspaper. Haaretz revisited the Six Day War of 1967, in which Israel seized not only the Palestinian territories of the West Bank and Gaza, but also a significant corner of Syria known as the Golan Heights, which Israel still refuses to relinquish.

The consensus in Israel is that the country’s right to hold on to the Golan is even stronger than its right to the West Bank. According to polls, an overwhelming majority of Israelis refuse to concede their little bit of annexed Syria, even if doing so would secure peace with Damascus.

This intransigence is not surprising. For decades, Israelis have been taught a grand narrative in which, having repelled an attack by Syrian forces, Israel then magnanimously allowed the civilian population of the Golan to live under its rule. That, say Israelis, is why the inhabitants of four Druze villages are still present there. The rest chose to leave on the instructions of Damascus.

One influential journalist writing at the time even insinuated anti-Semitism on the part of the civilians who departed: “Everyone fled, to the last man, before the IDF [Israeli Defence Forces] arrived, out of fear of the ‘savage conqueror’ … Fools, why did they have to flee?”

However, a very different picture emerges from Haaretz’s interviews with the participants. These insiders say that all but 6,000 of the Golan’s 130,000 civilians were either terrorised or physically forced out, some of them long after the fighting finished. An army document reveals a plan to clear the area of the Syrian population, with only the exception of the Golan Druze, so as not to upset relations with the loyal Druze community inside Israel.

The army’s post-war tasks included flushing out thousands of farmers hiding in caves and woods to send them over the new border. Homes were looted before the army set about destroying all traces of 200 villages so that there would be nowhere left for the former inhabitants to return to. The first Jewish settlers sent to till the fields recalled seeing the dispossessed owners watching from afar.

The Haaretz investigation offers an account of methodical and wholesale ethnic cleansing that sits uncomfortably not only with the traditional Israeli story of 1967 but with the Israeli public’s idea that their army is the “most moral in the world”. That may explain why several prominent, though unnamed, Israeli historians admitted to Haaretz that they had learnt of this “alternative narrative” but did nothing to investigate or publicise it.

What is so intriguing about the newspaper’s version of the Golan’s capture is the degree to which it echoes the revised accounts of the 1948 war that have been written by later generations of Israeli historians. Three decades ago – in a more complacent era – Israel made available less sensitive documents from that period.

The new material was explosive enough. It undermined Israel’s traditional narrative of 1948, in which the Palestinians were said to have left voluntarily on the orders of the Arab leaders and in the expectation that the combined Arab armies would snuff out the fledging Jewish state in a bloodbath.

Instead, the documents suggested that heavily armed Jewish forces had expelled and dispossessed hundreds of thousands of Palestinians before the Jewish state had even been declared and a single Arab soldier had entered Palestine.

One document in particular, Plan Dalet, demonstrated the army’s intention to expel the Palestinians from their homeland. Its existence explains the ethnic cleansing of more than 80 per cent of Palestinians in the war, followed by a military campaign to destroy hundreds of villages to ensure the refugees never returned.

Ethnic cleansing is the common theme of both these Israeli conquests. A deeper probe of the archives will almost certainly reveal in greater detail how and why these “cleansing” campaigns were carried out – which is precisely why Mr Netanyahu and others want the archives to remain locked.

But full disclosure of these myth-shattering documents may be the precondition for peace. Certainly, more of these revelations offer the best hope of shocking Israeli public opinion out of its self-righteous opposition to meaningful concessions, either to Syria or the Palestinians.

It is also a necessary first step in challenging Israel’s continuing attempts to ethnically cleanse Palestinians, as has occurred in the last few weeks against the Bedouin in both the Jordan Valley and the Negev, where villages are being razed and families forced to leave again.

Genuine peacemakers should be demanding that the doors to the archives be thrown open immediately. The motives of those who wish to keep them locked should be clear to all.