Cause and effect apply more happily to physical phenomena than to historical events. IMHO, cause and effect are not useful metaphors for understanding history; rocks do not have motives--people do.
Oh...and what makes for the motives of people?
What "caused" the "effect" of the 9-11 attacks? We have seen different reasons given:
Hatred of the U.S.
Jealousy of the U.S.
Our support of Israel.
Islamic Jihad.
...to name a few...
Or did God wave a magic want and POOF...it just happened?