The past eleven years have been difficult for terrorists. They lost their base in Afghanistan; much more of the world's intelligence, law enforcement, and military capacity is aimed at them than ever before. Homeland security in the United States and other countries is far more robust. The horror and tragedy that was 9/11 did many things; one of them was to galvanize this country and much of the world against terrorists and those who support them.
Still, the enemy is resilient. Weak states such as Somalia, Yemen, and Pakistan are a breeding ground; states at war with themselves, such as Syria, Afghanistan, and Iraq, are a magnet and a school for radicals who often are or become terrorists. Osama bin Laden is dead, but al-Qaeda and its offshoots live on. The Internet is a tool for radicalization, recruitment, and training. Homegrown terrorists are a real problem for even the most modern, democratic societies.
There are ways to react. Terrorists overseas can be targeted with drones and special forces. Weak states can be strengthened. Sources of money can be dried up. But terrorists will continue to emerge and strike until religious, political, and community leaders, along with parents, do all they can to make clear that terrorism is an illegitimate means of pursuing a political agenda. All of which is to say they will likely be around and active for a long time.
On occasion, terrorists will succeed despite our best efforts. That is part of the legacy of 9/11. But 9/11 also shows us that while terrorists can destroy, they are unable to create. They are not the inspiration behind the upheavals in the Arab world. Terrorists offer no alternative, only violence. On occasions they do succeed, it is essential that we show ourselves to be as resilient as they are and carry on. That is the other legacy of 9/11.