A member of the Saudi border guards mans a machine gun at the border with Iraq in July. Since the so-called Islamic State launched its offensive this summer in Iraq, Saudi Arabia has sent thousands of troops to the region. Faisal Nasser/Reuters/Landov hide caption

itoggle caption Faisal Nasser/Reuters/Landov

Alfons R. of Hamburg, Germany (shown in this undated photo), converted to Islam at age 17. Later, he went to Turkey, then Syria, to join ISIS. He was killed this past summer. Courtesy of Manfred Karg hide caption

itoggle caption Courtesy of Manfred Karg

Secretary of State John Kerry, left, Iraqi Prime Minister Haider al-Abadi, center, and Iraqi Foreign Minister Ibrahim al-Jaafari prior to a round table meeting of the global coalition to counter the Islamic State. Virginia Mayo/AP hide caption

itoggle caption Virginia Mayo/AP

Sunni tribesmen train on the outskirts of Ramadi, Iraq, on Nov. 16. Legislation authorizing a force of Sunni fighters drawn from Anbar province itself — modeled on the U.S. National Guard — has yet to be passed. Ali al-Mashhadani/Reuters/Landov hide caption

itoggle caption Ali al-Mashhadani/Reuters/Landov

The Islamic Youth Council in Derna, in eastern Libya, is among the local militant groups from Egypt to Libya that have reportedly pledged allegiance to the self-proclaimed Islamic State. Reuters/Landov hide caption

itoggle caption Reuters/Landov

Islamic State fighters march in Raqqa, Syria. The group has killed five Western hostages in recent months. In the 1990s, many radical Islamist groups gave interviews to journalists and refrained from kidnapping Westerners. AP hide caption

itoggle caption AP

Peter Kassig, who changed his first name to Abdul-Rahman when he converted to Islam, is shown with a truck filled with aid supplies for Syrian refugees. Courtesy of Kassig family hide caption

itoggle caption Courtesy of Kassig family

Iraqi Kurdish soldiers, or peshmerga, patrol an area in the recently recaptured town of Zumar, near Mosul in northern Iraq on Oct. 29. When the Islamic State captured the town in August, the Kurds fled. Now that the Kurds are in control, the Arabs are all gone. STR/EPA /LANDOV hide caption

itoggle caption STR/EPA /LANDOV

Demonstrators chant in favor of the Islamic State and carry the group's flags in Mosul, Iraq, in June. With videos, Internet magazines and social media, the group has effectively recruited throughout the world. AP hide caption

itoggle caption AP

Peshmerga look out from a front-line outpost — a few sandbags, soldiers, and grenades perched on the brow of a hill — to the eastern Iraqi town of Jalula. The Kurdish fighters are grappling with how to combat changing ISIS tactics. Alice Fordham/NPR hide caption

itoggle caption Alice Fordham/NPR

Aza Betwata (left) and his brother Mirwan (center) left Holland to join the Kurdish peshmerga fighting against ISIS militants in northern Iraq. Though the brothers come from a family of fighters, Aza had just two days of training — his brother must show him how to strip and clean his rifle. Alice Fordham/NPR hide caption

itoggle caption Alice Fordham/NPR

A family passes through Maktab Khaled in northern Iraq, the last Kurdish checkpoint before they make their way to Kirkuk. ISIS-controlled territory lies less than a mile away. Leila Fadel/NPR hide caption

itoggle caption Leila Fadel/NPR