The 1998 Fatwa was signed by Osama bin Laden, Ayman al-Zawahiri and others.
It lists three grievances:
1. U.S. occupation of the Arabian Peninsula.
"First, for over seven years the United States has been occupying
the lands of Islam in the holiest of places, the Arabian Peninsula,
plundering its riches, dictating to its rulers, humiliating its people,
terrorizing its neighbors, and turning its bases in the Peninsula into
a spearhead through which to fight the neighboring Muslim peoples.
2. U.S. aggression against the Iraqi people.
"Second, despite the great devastation inflicted on the Iraqi people by the crusader-Zionist alliance, and despite the huge number of those killed, which has exceeded 1 million... despite all this, the Americans are once against trying to repeat the horrific massacres, as though they are not content with the protracted blockade imposed after the ferocious war or the fragmentation and devastation. So here they come to annihilate what is left of this people and to humiliate their Muslim neighbors."
3. U.S. support of Israel.
"Third, if the Americans' aims behind these wars are religious and economic, the aim is also to serve the Jews' petty state and divert attention from its occupation of Jerusalem and murder of Muslims there. The best proof of this is their eagerness to destroy Iraq, the strongest neighboring Arab state, and their endeavor to fragment all the states of the region such as Iraq, Saudi Arabia, Egypt, and Sudan into paper statelets and through their disunion and weakness to guarantee Israel's survival and the continuation of the brutal crusade occupation of the Peninsula."
These three grievances are the motives for al-Qaeda's attacks.
All these crimes and sins committed by the Americans are a clear declaration of war on God, his messenger, and Muslims. And ulema have throughout Islamic history unanimously agreed that the jihad is an individual duty if the enemy destroys the Muslim countries.
The fatwa quotes shaykh of al-Islam, "As for the fighting to repulse [an enemy], it is aimed at defending sanctity and religion, and it is a duty as agreed [by the ulema]. Nothing is more sacred than belief except repulsing an enemy who is attacking religion and life." On that basis, and in compliance with God's order, we issue the following fatwa to all Muslims:
"The ruling to kill the Americans and their allies -- civilians and military -- is an individual duty for every Muslim who can do it in any country in which it is possible to do it, in order to liberate the al-Aqsa Mosque [in Jerusalem] and the holy mosque [in Mecca] from their grip, and in order for their armies to move out of all the lands of Islam, defeated and unable to threaten any Muslim."
Note: The above sentence is often quoted by U.S. officials using only the part in green with the part in red (the reasons why) omitted.
Look how ABC's movie "The Path to 9-11" resorted to FABRICATING a fatwa quote!