(1) Kosovo did not represent a "spread of Islam" - those Muslims had been living there for decades - as the old YR stats attest.
(2) Al-Qaeda has never mentioned America's religiously neutral stance in the Balkans as a contributing factor to their anti-American violence.
(3) The 9/11 conspirators had already been planning their attack for more than a year when we pushed out Milosevic.
(4) Muslim terrorists had already targeted the WTC six years before.
Your "theory" is just ridiculous on its face.
Not just decades...but centuries. Since the end of the 14th century, in fact.