The biggest powers in the world were not able to find a way to stop the war in Syria when it broke out in 2011.
More than four years on, a whole new set of challenges is coming from Syria, and other countries in the Middle East and Africa. And the world's biggest powers are struggling once again to find answers that work.
The new crisis is about refugees. The European Union is discovering, belatedly, that it is impossible to avoid the consequences of a range of wars and civil conflicts right next door.
Some Western politicians, and journalists, are taking proper notice for the first time of a refugee crisis that has been a huge concern for Syria's neighbours since the war started.
The difference now is that refugees, in big and increasing numbers, are trying to get to the richest countries in Europe.
The EU is discovering that the Mediterranean is an inadequate moat. Eventually a response will be found to handle this summer's refugees.
But the fundamental reason why they will continue to come is still there.
And that is war in Syria, in Libya, in Iraq and Yemen. Violence, instability and chaos make lives miserable, dangerous and short across a broad swathe of the Middle East and Africa. It is not surprising that people want to get out.
Some may not have their lives threatened directly, but they want to leave before the worst happens.
People do not leave their homes lightly. They flee, and sometimes take dreadful risks at the hands of people smugglers, because the alternatives are so much worse.
I walked through the ruins of Yarmouk, one of the most fiercely contested battlegrounds in Damascus, only a few miles from the centre of the city.
Yarmouk used to be a Palestinian refugee camp for families who had fled or been driven from their homes when Israel won its independence war in 1948.
Over the last three years in Damascus I have spent nights watching Yarmouk being pounded. On the day I was there, it was quiet and eerie.
The Syrian army and Palestinian fighting groups control roughly half of Yarmouk. All the civilians who lived there have gone. Some are in shelters nearby. Some are trying to get to Europe.
Street after street was in ruins. Every building was damaged, not just by artillery but by thousands of rounds that were fired in street fighting.
Inside the buildings soldiers hacked holes in dividing walls between flats so they wouldn't have to risk the streets.
Jeremy Bowen reports from inside Syria
Four hundred metres away from where I was, fighters from Islamic State and the Nusra Front, the al-Qaeda affiliate, were in control.
An unknown number of Palestinian civilians, in their thousands, are trapped there too.
UNRWA, the UN agency that looks after Palestinian refugees, has not been able visit them with relief supplies since March. As well as bullets and shells, this summer they have to endure a typhoid outbreak.
'Three Big Macs'
What has happened to Yarmouk is just a single example of why so many have wanted to leave Syria.
Some who left Syria earlier in the war hoped they would return home fairly soon. Now that the war is in its fifth year, they have realised that is not going to happen anytime soon. They need to find another future.
And until a way is found to make things better in Syria, they will keep leaving. Peace is too much to ask. Some stability might help.
One senior aid worker in Damascus complained that European countries who are preparing to spend billions of euros on absorbing refugees might have headed off the problem, or at least persuaded more to stay in the region, if they had fully funded a succession of appeals for humanitarian operations in and around Syria.
The aid worker said messages had been sent warning European governments that conflict and desperation would force refugees to head their way.
Inside Syria, the UN's World Food Programme (WFP) has cut rations and is struggling to find $12.50 (£8) per head to spend on food for each of Syria's four million displaced people every month.
"That's the price of three Big Macs in Europe," the aid worker said. "But we can't do it."