1) Israel (a racist, religious, apartheid state dealing with frequent human rights violations) and Zionist Jews for pushing the pro-Israeli foreign policy through AIPAC, the 2nd most powerful lobby in the U.S., an agent of a foreign nation not being required to register as an agent of a foreign nation. American politicians are scared shitless of AIPAC. Very few people have taken a stand against it, and every time the Jews cry anti-Semitism etc. You don't go against the Jews in USA and make it in life.
Here's the Walt and Mearsheimer paper, an essay on the powerful Israeli lobby by two high profile people, and no, they're not *haters* in any way.
http://ksgnotes1.harvard.edu/Research/wpaper.nsf/rwp/RWP06-011/$File/rwp_06_011_walt.pdf
You cannot ad hominem it and it's a very meticulously researched paper, and a must read for anyone who wants to understand what's going on.
2) The Arabs that hijacked the planes, crashed them into the buildings, buildings fell as a result. No conspiracy theories, no controlled demolition, no invisible gnomes wiring explosives to the buildings, no aliens, no such bullshit. You probably expected this to be a conspiracy response, sorry in that case. Their motivation, as their leaders have claimed, was U.S.' pro-Israel foreign policy. Israel is an engine of chaos in the Middle East, as anyone with half a brain might figure out.
3) The Americans who've let this happen to the government, and especially the neocons. Technically you should have fought against your government or elected people who'd stop this madness. As a result, determined Arabs have attacked you mildly. It's nothing compared to what your support for Israel has done for them. Also, it should be noted, that the Arabs didn't attack you for religious reasons, they've attacked you for invading their land. It's territorial, it's not a religious conflict.
Protip: Try a non-interventionist foreign policy. It'll make the world and especially you happy. Both morally and economically. Also, bringing 'democracy' in the Middle East and that bullshit won't change anything into good. What you actually seek is to destroy their lives. You tell me, how will bringing democracy change what a Palestinian kid KNOWS about Israel?
In b4 Muslim, self hating Jew, White supremacist, sand nigger, Holocaust denier, hater, racist blah blah blah, but you can't really dispute much of what I say.