(CNN) – The attack that killed 14 people in San Bernardino, California, in December 2015 marked the deadliest terrorist attack on U.S. soil since September 11, 2001.

It also underscored an unsettling reality: ISIS has morphed from a scourge affecting Iraq and Syria to a threat to people around the world.

Since declaring its caliphate in June 2014, the self-proclaimed Islamic State has conducted or inspired over 60 terrorist attacks in 20 countries other than Iraq and Syria, where its carnage has taken a much deadlier toll; those attacks outside Iraq and Syria have killed at least 1,160 people and injured more than 1,700 others.

One San Bernardino killer pledged allegiance to the ISIS leader, investigators say. And ISIS hailed the attackers as “martyrs” and “supporters.”