How were the September 11 terrorist attacks unique when compared to other terrorist attacks?
What was truly unique about these attacks was the detailed planning that went into them and the scope of action that was contemplated. Previous terrorist attacks had been relatively simple things. A group of terrorists would hijack an airplane and demand the release of prisoners. A government official would be assassinated or kidnapped. These were not particularly complicated and were relatively small scale things. But the 9/11 attacks were much different. They involved serious amounts of training for the attackers. They aimed to kill thousands of people and to destroy major landmark buildings. These were much bigger and more detailed attacks than anything that had come before.