A 3-year-old boy washes ashore on a Turkish beach. Seventy-one migrants suffocate in a truck in Austria. Daily scenes of chaos unfolding in European cities as governments try to halt a human tide heading north. There seems to be no letup to the horrors triggered by Syria's civil war.

The images have sparked an international uproar over the human cost of the crisis and spurred calls for serious action to end the country's long-running war.

Here's a look at the conflict and what compels Syrians to attempt the treacherous journey to Europe.

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WHAT ARE THEY ESCAPING?

Barrel bombs, chemical weapons attacks, beheadings and starvation — to name just a few. Most of the refugees are driven by an overriding need to escape what has essentially become hell on earth, caught between Syrian President Bashar Assad's ruthless war machine and the Islamic State group's brutality. Many Syrians say most unbearable are the barrel bombs dropped daily on opposition-held areas by Syrian army helicopters. The makeshift, shrapnel-packed explosive devices known by Syrians as death barrels pulverize entire neighborhoods once they hit the ground. They have killed tens of thousands of people over the past four years, according to human rights organizations. Islamic State militants have also been responsible for the exodus out of Syria. The militant group's takeover of a key town on the Turkish border in June, for instance, triggered a rush of desperate refugees pouring into Turkey, with some throwing their children over the border fence in a desperate attempt to get them to safety.

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WHAT ARE THE NUMBERS?

Syria's brutal conflict, now in its fifth year, has touched off the greatest humanitarian crisis of our time, according to U.N. officials. The organization estimates that around 250,000 people have been killed and more than one million wounded since March 2011. About half the country's prewar population of 23 million has been displaced, including more than 4 million who have fled Syria. Tactics such as encircling populated areas have caused untold cases of starvation, malnutrition and chronic illness. The U.N. refugee agency says Syria is the leading source of refugees, pushing Afghanistan — which had held that status for more than 30 years — down to second place. A U.N. report released Thursday said more than 2,000 Syrians refugees have drowned in desperate efforts to reach safety in Europe since 2011.

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WHY DO THEY GO TO EUROPE?

For many Syrians, a perilous journey to Europe with an uncertain future is better than certain death in Syria. Many say their overriding goal is to secure a better future for their children. Some of Syria's neighbors, which initially took in hundreds of thousands of refugees, say they can no longer afford to host them. Some have closed their borders while others are enforcing restrictions that increasingly make it difficult for them to stay or find work. Gulf countries are not taking refugees, and countries like Iraq and Lebanon are unstable, making the idea of life in Europe more appealing.

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WHAT WILL IT TAKE TO END THE WAR?

The war has defied all attempts for a diplomatic solution. Unimaginable suffering has unfolded while the world stands witness. The emergence and spread of the violent Islamic State group as the most potent opposition to Assad has led to renewed diplomatic activity to try and end the war. The U.N. envoy to Syria has called for a new round of talks and is trying to set up working groups aimed at facilitating a political process. That effort faces opposition from both Assad and his opponents, both of whom still hope they can settle the conflict through military force. Iran is also trying to mediate, but as a key backer of Assad, any initiative from Tehran is likely to be stillborn. Assad is unlikely to step aside, and without serious pressure from their regional and international supporters, the rebels trying to topple him are unlikely to accept a political transition which includes him.

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WHAT CAN THE WORLD DO NOW?

Only an end to the war in Syria will stop the flow of refugees. The haunting images of drowning migrants have sparked a public outcry and calls for world leaders not only to change their attitude toward refugees but to deal with the root cause of the crisis. But the war is unlikely to end anytime soon unless countries that sponsor either side of the Syrian divide come together and convince their partners of the need to agree on a power sharing agreement. Other measures such as safe zones inside Syria may help stem the exodus, but will not end it.