That being said there are a lot of reasons.
-The US was in the Baltic Peninsula, and Osama wasn't happy about that, as it was considered Muslim holy ground.
- Osama also hated the Western way of life. (equality for women, free speech, lust)
- The Book of Islam talks about a Jihad, which means struggle. Extremists can see this as a struggle against non Muslims.
The effects were wars and domestic policies.
- The US invaded Afghanistan to stop Al Qaeda and the Taliban. Keep in mind Al Qaeda attacked the towers, the Taliban was in control of the government and was helping Al Qaeda because they had similar beliefs.
- The Patriot Act was created to help stop terrorism. It is up to debate how much it really did.
- The Department of Homeland security was created to to stop terrorism. Again, its up for debate if it is necessary.
- Also the TSA was created and airline security was more strict, For example, they had air marshals who were paid to sit on planes just in case.
if you are doing a report you will have to research these things more, because this is just an outline. Google your question and you will find the results you want.
US foreign policy.
The people who commited the murders had 3 stated demands. They wanted a complete removal of all US troops from the Kingdom of Saudi Arabia, they wanted the US to stop supporting the various dictators in the region, and they wanted an end to US support for Israel.
The causes-Clinton didn't go after Bin Laden. Effects-people suddenly remembered they were Americans and went out an bought patriotic crap made in China.
The cause: GREED - the rich and powerful want more and more. The effects: It got American into war which poured trillions of $$$ (and power) into the hands of the already drunk with power Rich ppl.
Please be as specific as you can. You are welcome to give me a website link for more information, but tell me something. Please don't just post the link as your answer.
If you aren't going to give me a reasonable answer, don't waste your time or my time. Just move on to another question.
