In 2012, the Obama administration, engaged in a presidential race tainted by the messy security vacuum left after intervening in Libya, rejected the idea of a no-fly zone against the Assad regime in Syria. So Syrian jihadists, backed by thousands of foreign fighters, created their own: They carved out a safe haven by seizing government airbases and by pushing out more moderate rebel groups. The grim results are what we see before us today.

America's airstrikes inside Syria against both the Islamic State, often known as ISIL, and Al Qaeda's primary affiliate in Syria, Jabhat al-Nusra, come with some obvious benefits — taking on a genuine threat to U.S. interests and security — but may also expose the United States to some unintended consequences — dangers that could haunt the United States for years to come.

Some of these dangers are apparent and some less obvious. As of July, more than 12,000 foreign fighters had flocked to Syria, hundreds bearing passports that could allow them to slip in and out of Western countries unnoticed. ISIL members in the region, or ISIL supporters globally, might soon conduct reprisal attacks against U.S. personnel and facilities abroad and could launch dangerous attacks in Europe or even against the U.S. homeland. The United States might see a hurried, conventional weapons attack by an unconnected but inspired supporter or, in the worst case, a former foreign fighter with sufficient skill and experience to hit a soft target like a transportation hub or shopping center.

Whatever the scenario, in taking the lead against ISIL, the United States has painted a bull's-eye on its citizens. A more indirect U.S. strategy to counter ISIL with proxies and supporting allies could have deflected the group's most passionate members from hitting the U.S. homeland. But now, the United States has moved itself up in ISIL's targeting priorities, from one of many to the very top of the list. Abu Muhammed al-Adnani, ISIL's official spokesman, said in an official statement released this week, "O Americans, and O Europeans, the Islamic State did not initiate a war against you, as your governments and media try to make you believe. It is you who started the transgression against us, and thus you deserve blame and you will pay a great price."

Clint Watts is senior fellow at the Foreign Policy Research Institute in Philadelphia and the Homeland Security Policy Institute at the George Washington University. Clint served previously as executive officer of the Combating Terrorism Center at West Point.