Even before the Paris attacks, the United States and its allies escalated airstrikes against the Islamic State’s oil facilities in eastern Syria. Hundreds of tanker trucks, carting oil to markets in Turkey and Iraq, have also been bombed as part of a plan to cripple production. Apart from this effort, the challenge now is attacking the group’s sources of revenue that extend far beyond oil.

The Islamic State, also known as ISIS or ISIL, may be the best-financed terrorist franchise in history. In the territory it controls in Iraq and Syria, it extorts hundreds of millions of dollars a year in “taxes,” tolls, and profits from businesses and residents, as reported by The Times. It also earns millions by looting banks, through ransoms for kidnap victims, and selling plundered antiquities.

All of this makes it harder to close off the money spigot, but the United States and its allies can claim some success. For example, this summer the Americans finally persuaded the Iraqi government to stop paying salaries to public employees in at least one ISIS-controlled province, which meant the group could no longer extort huge sums from those workers.

Oil is still a major income source, bringing in an estimated $40 million a month before the latest airstrikes. Oil fields and facilities were an early target when the American-led campaign began in August 2014. Washington, however, pulled back as it tried to balance fighting the Islamic State and maintaining energy supplies for civilians. That measured approach may no longer make sense, given the widening threat posed by the group.