Add in al-Nusra Front (who is a separate group from the Islamic State of Iraq and the Levant) and Syria has by far the highest concentration of jihadis in the world, and we are shipping weapons into this cauldron of terror thanks to Obama.

BEIRUT — A rebranded version of Iraq’s al-Qaeda affiliate is surging onto the front lines of the war in neighboring Syria, expanding into territory seized by other rebel groups and carving out the kind of sanctuaries that the U.S. military spent more than a decade fighting to prevent in Iraq and Afghanistan.

In the four months since the Iraqi al-Qaeda group changed its name to reflect its growing ambitions, it has forcefully asserted its presence in some of the towns and villages captured from Syrian government forces. It has been bolstered by an influx of thousands of foreign fighters from the region and beyond.

The group, now known as the Islamic State of Iraq and the Levant, is by no means the largest of the loosely aligned rebel organizations battling to overthrow Syrian President Bashar al-Assad, and it is concentrated mostly in the northern and eastern provinces of the country. But with its radical ideology and tactics such as kidnappings and beheadings, the group has stamped its identity on the communities in which it is present, including, crucially, ­areas surrounding the main border crossings with Turkey.

Civilian activists, rival rebel commanders and Westerners, including more than a dozen journalists and relief workers, have been assassinated or abducted in recent months in areas where the Islamic State has a presence.

With multiple groups competing for influence, the Islamic State cannot be held responsible for all the incidents that have occurred in Syria. Jabhat al-Nusra, the original Syrian al-Qaeda affiliate, which has resisted efforts by the Islamic State to absorb it, maintains a robust presence in many parts of the country. Criminal gangs also have taken advantage of the vacuum of authority to carry out kidnappings for ransom, mostly of Syrians.

But at a time when the Islamic State is undergoing a revival in Iraq, killing more people there than at any time since 2008 and staging a spectacular jailbreak last month that freed hundreds of militants, the push into Syria signifies the transformation of the group into a regional entity. The U.S. military — which referred to the organization as al-Qaeda in Iraq (AQI) — claimed it had subdued AQI by the time the United States withdrew from Iraq in 2011.