Today, three weeks later, the political dispute is only just starting about what were the main causes of the mass flight. According to the Croatian government, backed by many Western diplomats, the exodus was primarily the result of an order from the Krajina Serb leadership to evacuate.
However, the truth is more confused and more tragic. The evidence from interviews with Serb refugees, Serbs and Croats still in the area and international observers, suggests that the civilian flight was in large part caused by mass panic and fear. Although there is evidence that the Krajina Serb leadership in the southern part of the region ordered a military retreat soon after the shelling began, there is no proof that they had prepared for a civilian evacuation.
Serb refugees accuse their leaders of betrayal, by taking to their heels and leaving civilians to face Croat revenge or find their own means of escape. The evidence points to a cynical betrayal of Serb civilians and Serb soldiers by the Serbs' own leaders, combined with a deliberate policy on the part of Croatia to terrorise the population into flight.
There is growing reason to believe that the 150,000 Serbs were sacrificed as part of a Croat-Serb territorial deal. The debate over what caused them to flee is of fundamental importance. It will influence the shape of a new political settlement in the region, and will dictate whether refugees from the conflict, whether Serb, Muslim or Croat, will be given the right to return one day to their homes or win compensation. The view taken by Western leaders on the issue will also indicate how far, in their desperate efforts to achieve peace, they are prepared to condone what amounts to "ethnic cleansing".
In the specific context of the refugee debate, the Krajina exodus bears comparison with the flight of Palestinians during the 1948 Arab-Israeli war, which brought about the creation of Israel. Croatia claims - as has Israel since 1948 - that the refugees fled largely of their own accord, under instructions from their leadership. If Croatia can convince the world of this, it will reduce the chances that the refugees will be able to claim a right of return. As with the Palestinians, however, the stories of the refugees bear little relation to the account of the victorious power.
The Middle East has been debating the truth about the Palestinian flight for nearly half a century. It is depressing to observe that only three weeks after the Croatian offensive, the issues here are already being muddied. As the Palestinian experience has proved, however, the grievances of refugees do not go away. The right of return remains an important barrier to a final settlement in the Middle East, and Palestinian refugee camps are still seed-beds of violent revenge.
The flight of the Krajina Serbs was astonishing: in the space of 24 hours, 150,000 people, some of them farmers, some prosperous businessmen, gave up their livelihood. The majority came from families who had lived in the area for generations. Before the 1991 war the Serbs, who comprised the majority population in most parts of the Krajina area, lived relatively peacefully alongside the Croats. Some of the refugees were born of mixed marriages, and there were even Croats among those who fled, usually married to Serbs. Some of the houses set ablaze after the exodus belonged to Croats with Serb spouses.
"My parents had a successful business in Knin," said Predrag Sare, a 23-year-old interpreter. "They had worked all their lives to build a nice house. They were not really interested in politics. They were interested in building their lives and were quite well off."
Mr Sare was separated from his family and sought refuge in the UN base in Knin. "Now they are in Belgrade. They just fled in fear, and gave everything up."
What emerges from the interviews is a story of a civilian population which was not driven out, but which was given no choice but to flee.
The Krajina Serbs had been given to believe the land would be defended, and had received no instructions to take shelter or evacuate. According to several of those questioned, the Krajina Serb leader, Milan Martic, announced that the defences would hold in a broadcast on the eve of the bombardment. The same day Peter Galbraith, the US ambassador to Croatia, announced the possibility of a last-ditch peace settlement. "This led people to think perhaps the attack would not happen," said a UN official in Krajina.
The people of Knin were in bed when the bombardment began early on 4 August. When the shelling spread to the north, people were eating or working - as could be seen from the scattered debris of the sudden flight, which belies claims by one senior Western diplomat that the people had been "practising evacuation".
Most significantly, perhaps, even regular soldiers in the Krajina Serb army were confident, until the offensive began, that Croatia would be repelled. "We were led to believe that our defences would hold. We knew we had a strong army," said a Serb soldier who was on duty in the town of Drnis.
Twenty-four hours later this soldier was fleeing in abject fear, along with 150,000 other Serbs. There were several reasons for such immediate, widespread flight. First, shells were pulverising the area; more than 2,000 shells fell around Knin alone, in a blitz which UN military observers believe was designed to create maximum civilian terror. The Croatian advance was designed to drive the civilians ahead of it.
Second, within 24 hours of the shelling, the Krajina Serb military leaders appear to have ordered at least some of their forces to withdraw and evacuate. The civilian panic intensified when people realised their forces were not resisting and had even fled. The order for the Serb military in the UN Sector South to pull out appears to have been given in the early hours of 5 August.
It is entirely possible that the Serb leaders knew very well that a military retreat would trigger a flight of civilians. The soldiers' families were among the first to leave, and their departure must have fuelled panic among their neighbours. However, even by the next day there was no sign of a general evacuation order.
"Many of the Serb troops were themselves unaware of the order to retreat, and there were no instructions to civilians. Everyone was so scared," said an elderly Serb who had stayed in his house.
Perhaps the most important reason for the fear, however, was the dread that Croatia would wreak terrible revenge if it regained the land. For four years Krajina Serb leaders had been pumping the population with paranoid fears of the Croatian "Ustasha", as they called Croats.
The Serbs who captured Krajina in 1991 destroyed Croat property and forced Croats to flee. By the time the shelling started, all Serbs in the area feared that they would be held to account for these crimes. "We all feared the revenge," one young Serb student said.