Hundreds of thousands of immigrants, fleeing violence and poverty in Africa and the Middle East, are trying to find a better life in Europe – putting major strains on the EU and its member states.
Even as the US and Turkey agree on trying to drive the Islamic State away from the Syrian side of the border with Turkey, there are as many agendas as there are players trying to shape the conflict.
Turkey has long sought a buffer zone in northern Syria. Critics say it is exploiting the US-led battle against Islamic State militants to strike at Kurdish forces in Iraq and Syria that it sees as a threat to Turkish rule.
The airstrikes were prompted by intelligence indicating a likely Islamic State attack. The US said a deal has been reached with Turkey to use a key airbase.
Little is known about the Khorasan group, though it is said to be a small, elite group of Al Qaeda members involved in planning high-level attacks on the US.
The humanitarian crisis is deepening and the chances of a political solution soon seem very slim.
The fighting marks the most intense rebel attack in three years in the bitterly contested city.
While the jihadis of the Islamic State hope their reputation for brutality will deter their enemies, another group's snuff video shows that what has happened instead is an expansion of viciousness and cruelty.