What was al-Qaeda's goal in perpetrating the September 11th Attacks?

Answer 1

GOALS OF AL-QAEDA IN GENERAL
Al-Qaeda is an international post-national terrorist organization. Al-Qaeda's mission is to bring about the Fall of the West and the Islamicization (both cultural, religious, and political) of Western Nations. Their organization sought refuge in several Arab and Muslim countries and found space to grow in Afghanistan until the American Invasion in 2001. Since that point, they have grown cells in numerous other countries, but focused their greatest efforts in Franchising. Al-Qaeda's end-goal is the international "liberation" of much of the world from "hedonism" and "modernity" to an Islamic theocracy.. This new government would be an Islamic Caliphate that either that controls a significant percentage or all of the Islamic World or the entire planet.

SPECIFIC GOALS OF SEPTEMBER 11TH
There were several distinct purposes for which al-Qaeda perpetrated September 11th specifically, along with the general goals of al-Qaeda mentioned above:

1) Demonstration of Potency: The destruction of the Twin Towers and the attacks on the Pentagon and White House (which was foiled by the brave actions of the hostages) were symbols of the actual capabilities of the al-Qaeda organization. It took intense levels of planning, including pilot training, chemical training, rehearsal, and weaponry to be able to find and take advantage of weaknesses in the security of the most powerful nation on the planet.

2) Demonstration of Willpower: The choice of the 19 hijackers to take their own lives for what they believed and kill many people in the process was a demonstration of the commitment of their beliefs concerning the destruction of the West and martyrdom to God.

3) Create a Discussion about Islamism and Jihadism: Prior to the September 11th Attacks, Jihadism (the belief in installing an Islamic-Law country using violence) was not often discussed outside of the Middle East and, even in those regions, it was ignored. The substantial impact of September 11th meant that these issues would become far more prominent and, "hopefully" -- from the al-Qaeda perspective, embrace the Jihadist ideology.

4) Gain Attention as a Flag-Bearer: This follows from the previous point. Since al-Qaeda performed this foremost Jihadist attack (September 11th), it signaled to all would-be or present Jihadists that al-Qaeda was the most powerful, most organized, and most important Jihadist organization. In this way, al-Qaeda could recruit for new terrorists. It was effectively a "resume-builder" for the organization.

5) Death to the Infidels: Of course, no discussion of September 11th would be complete without discussing the belief that al-Qaeda members had concerning the people in the buildings that they attacked and planes that they hijacked. Al-Qaeda believed very strictly that those people who did not believe as they did were infidels and not worthy of living. They argued that the Qur'an is opposed to the continued freedoms that these people enjoyed, most especially the freedom of conscience to reject Islam as the correct religion. (Most Muslims do not agree with this perspective, which is why most Muslims do not butcher people.)

6) Entry to Paradise: Finally, by performing an act of jihad (striving/fighting in the name of God), the members of al-Qaeda believed that they were going to die martyr's deaths. According to most Islamic sources, the most-assured way to enter paradise/heaven is to be killed as a martyr while fighting in a jihad. Where Jihadist philosophy diverges from traditional Islam is that suicide attacks, e.g. guaranteed death for militant action against infidels, qualifies as martyrdom. Most scholars argue that suicide disqualifies the act of martyrdom; there must be at least some chance of surviving the battle or engagement for the death on the field to be considered an act of martyrdom. (Scholars also argue that killing noncombatants is not a proper jihad, but this is a distinct and more divisive issue in Islamic circles.)