Why? The attackers were Islamic terrorists from other nations. According to what has been said by Osama bin Laden´s al-Qaeda terrorist group and organization. They were trying to act in retaliation for America's support of Israel. Its involvement in the Gulf War and its continued in the military company in the Middle East. Some of the terrorists had lived in the United States for more than a year and had taken flying lessons at American flight schools. Others had slipped into the country through the Middle East airports, months before September 11 and acted as the backup of the operation. It´s been said they have been planning this for more than two years. Khalid Shaikh Mohammed was the central planner of 9/11 and one of the leaders of the al-Qaeda organization. Everyone that attacked was mostly from Israel.