<<"They " have never said that they have this limitation on their ambition.>>
I've read numerous accounts of Resistance fighters who took up the gun in response to a specific grievance, such as Palestine, Chechnya, the invasion of Iraq, the establishment of U.S. bases in Saudi Arabia, etc. Without any logical justification, you claim a wider goal for each of them. Pure projection (THEY want world domination, when in fact that goal is way more consistent with U.S. actions than with anything most of the Resistance fighters ever said - - but the Israel Lobby keeps a huge amount of "scholars" on its gravy train, combing through every speech of every lunatic, looking for the magic words "global jihad" or "global Sharia" so that the U.S. military-industrial complex and its media claque can happily serve up the results of all this research to "prove" that "They're out to get us" when every objective fact points to relentless exploitation, subversion, interference and ultimately invasion BY THE WEST of Muslim lands, going on for decades, ever since the collapse of the Ottoman Empire.)
<<Why do they attack the USA at all , if their real aim is more local?>>
Why bomb Cambodia if the real aim is Viet Nam? Why bomb Germany when you want to liberate Occupied Europe? Why shoot for the head of the dragon when it's his claws that are going to rip you to shreds?
<<The Shah of Iran was deposed without burning down downtown New York , so why does such a thing help them take over Saudi Arabia?>>
Later day, better tactics. They're starting to get their shit together. In the Vietnam years, the idea was "Bring the War Home!" meaning that as long as war meant that Vietnamese children would be roasted to death in napalm while New Yorkers sipped lattes on West 57th Street, the American people would tolerate the war forever. Once things started to blow up in America, the people would start asking questions about the war that they should have started asking years before.
Now the war on the Muslims and the theft of their resources is starting to cost America big-time. I'm not talking about the 4,000 dead hillbillies nobody but their families will ever miss - - I'm talking three trillion bucks and counting plus the cost of "Homeland Security" and the loss of American prestige around the world. IMHO, the al Qaeda tactic has already succeeded brilliantly by raising the cost of American aggression exponentially. Which was the theory behind "Bring the War Home!"