ISIS has been known to kidnap large numbers of workers and execute those who they believe are working with the Assad Regime. Not only do they bring in hundreds to basically indiscriminately execute, but they also have been known to take women as sex slaves and kidnap for ransom.
NPR says that the "extremists have faced setbacks as Assad's forces push the group further from the densely populated area around the capital," which could have caused them to seek actions like kidnapping. "Syria's minister of industry says his office is working to free hundreds of workers." The death toll in the year 2015 was mostly civilian and it should be cause for concern as the Islamic State is terrorizing innocent people.
After the Islamic State claimed responsibility for the attacks in Brussels, there haven't been many changes or new ways to combat these terrorists. There have been countless, covert U.S. airstrikes and a lot of controversy but not much direct and effective action. I don't mean to post another "what do we do about ISIS" post, but what should we do about ISIS. Do we interfere with activity in other countries in attempt to do the right thing? Does our involvement in foreign affairs only get people and nations to hate us more (go out to find WMD's but kill thousands of civilians and turn out empty handed)? Or is it a mistake to be stand by and watch a country to get it's stuff figured out over the course of nearly five bloody years?