Can ISIS be stopped: an international coalition vows to defeat the terrorist group, but the challenges are enormous.

• Author: Brown, Bryan
• Position: INTERNATIONAL - Islamic State

If there's one thing world leaders can agree on, it's that ISIS must be crushed

Over two weeks this fall, the terrorist group killed nearly 400 people in attacks in three different countries: A Russian passenger jet was blown up over Egypt; a calm Friday evening in Paris was shattered by terrorists detonating explosives and firing into crowds at restaurants and a concert; and suicide bombers unleashed the deadliest attack in Beirut, Lebanon, in 25 years. And in December, a Muslim couple in the U.S., claiming allegiance to ISIS but apparently acting on their own, killed 14 people and wounded 21 others in San Bernardino, California.

These are just a few of the atrocities that ISIS--the Islamic State of Iraq and Syria, also known as the Islamic State or ISIL--has been linked to in recent years. The radical Islamist group has seized large swaths of Syria and Iraq, where it's trying to create its own state (see map, p. 10). There, it has imposed laws based on "a strict interpretation of Islam.

ISIS's stated ambition is to re-establish an Islamic caliphate like the ones that ruled the Middle East and North Africa in past centuries. But recently it's also made it clear that it intends to wage a holy war with the West. After the attacks in France, ISIS issued a warning: The events were merely the "first of [a coming] storm."

Now the world is vowing to fight back. ISIS "cannot be tolerated," President Obama declared following the attacks in France. "It must be destroyed."

The day after the Paris attacks, representatives from 17 countries met in Vienna, Austria, and promised to coordinate their efforts to defeat ISIS.

Executions & Beheadings

But that will require uniting longtime rivals such as the U.S, and Russia, and Iran and Saudi Arabia. Beyond that, it means addressing a complex set of problems in the Middle East.

ISIS is the product of recent chaos in the Arab world, and it also feeds off centuries of sectarian strife within Islam. ISIS followers are Sunni Muslims, and the group considers Islam's other major sect, the Shiites, to be infidels. That's why ISIS sees the Shiite-led governments of Iraq and Syria as enemy states.

In 2011, a civil war broke out in Syria, with many rebel groups--including some that had U.S. support--fighting against Syria's tyrannical Alawite * president, Bashar al-Assad. ISIS, which began as an A1 Qaeda affiliate in Iraq, took advantage of the chaos and started seizing territory in Syria. With its brutal tactics--including on-the-spot executions and public beheadings of opponents--ISIS became the most powerful of the rebel armies there.

"As ISIS won victory after victory and took more and more territory, it attracted fighters from all over the world," says political scientist Karl Kaltenthaler of the University of Akron, in Ohio.

In December 2013, ISIS pushed back into Iraq, conquering territory about the size of Great Britain. ISIS terrorized regions under its control, forcing Christians and religious minorities to convert or die, and selling thousands into slavery. It seized oil refineries and stole $425 million from Iraq's central bank. Six months later, the group's leader, Abu Bakr al-Baghdadi, declared all land under its occupation the new caliphate of the Islamic State.

In many ways, ISIS has functioned as a real, organized state. It has proved adept at financing itself by selling oil, collecting kidnapping ransoms, and heavily taxing people within its territory.

Through sophisticated social media programs targeting disaffected Muslims around the globe, ISIS has attracted thousands of recruits worldwide--including an estimated 4,000 Westerners, about 250 of them American. As was apparently the case with the San Bernardino attackers, ISIS has inspired some people to carry out terrorist attacks in its name (see 'A New Threat at Home, " facing page).

8,000 Airstrikes

It's clear that ISIS's influence is spreading. While most experts believe ending the Syrian war is key to stopping ISIS, tensions run high over how to do it.

Years of costly U.S.-led wars in Iraq and Afghanistan have left many Americans wary of getting stuck in another conflict. Although President Obama has refused to send ground troops to Syria, he authorized bombing raids in August 2014. Since then, the U.S. and its allies have conducted more than 8,000 airstrikes on ISIS targets.

Until the most recent terrorist attacks, Obama's goal had been to "contain" ISIS within its territory. Some experts think that's the best way to gradually reduce its influence. But others blame Obama's caution for allowing the group to grow.

Most of the 2016 presidential candidates have called for a more aggressive fight with the enemy.

Republican Marco Rubio wants the U.S. and other nations to send ground troops. "We will only be able to protect our people at home if we defeat [ISIS] abroad," he says.

"Our goal is not to deter or contain ISIS, but to defeat and destroy ISIS," says Democrat Hillary Clinton.

The challenge of getting American leaders to agree on how to...