Here is a mild, brief explanation to answer the question: why??
I am certainly not minimizing the loss of life, anguish and fear being experienced by americans and canadians.
The following is from this address
http://www.guardian.co.uk/Archive/Article/0%2C4273%2C4255855%2C00.html
S
Americans Can't Understand
Why They Are So Hated
By Seumas Milne
The Guardian - London
9-16-1
Nearly two days after the horrific suicide attacks on civilian workers in New York and Washington, it has become painfully clear that most Americans simply don't get it. From the president to passersby on the streets, the message seems to be the same: this is an inexplicable assault on freedom and democracy, which must be answered with overwhelming force - just as soon as someone can construct a credible account of who was actually responsible.
Shock, rage and grief there has been aplenty. But any glimmer of recognition of why people might have been driven to carry out such atrocities, sacrificing their own lives in the process - or why the United States is hated with such bitterness, not only in Arab and Muslim countries, but across the developing world - seems almost entirely absent. Perhaps it is too much to hope that, as rescue workers struggle to pull firefighters from the rubble, any but a small minority might make the connection between what has been visited upon them and what their government has visited upon large parts of the world.
But make that connection they must, if such tragedies are not to be repeated, potentially with even more devastating consequences. US political leaders are doing their people no favours by reinforcing popular ignorance with self-referential rhetoric. And the echoing chorus of Tony Blair, whose determination to bind Britain ever closer to US foreign policy ratchets up the threat to our own cities, will only fuel anti-western sentiment. So will calls for the defence of "civilisation", with its overtones of Samuel Huntington's poisonous theories of post-cold war confrontation between the west and Islam, heightening perceptions of racism and hypocrisy.
As Mahatma Gandhi famously remarked when asked his opinion of western civilisation, it would be a good idea. Since George Bush's father inaugurated his new world order a decade ago, the US, supported by its British ally, bestrides the world like a colossus. Unconstrained by any superpower rival or system of global governance, the US giant has rewritten the global financial and trading system in its own interest; ripped up a string of treaties it finds inconvenient; sent troops to every corner of the globe; bombed Afghanistan, Sudan, Yugoslavia and Iraq without troubling the United Nations; maintained a string of murderous embargos against recalcitrant regimes; and recklessly thrown its weight behind Israel's 34-year illegal military occupation of the West Bank and Gaza as the Palestinian intifada rages.
If, as yesterday's Wall Street Journal insisted, the east coast carnage was the fruit of the Clinton administration's Munich-like appeasement of the Palestinians, the mind boggles as to what US Republicans imagine to be a Churchillian response.
It is this record of unabashed national egotism and arrogance that drives anti-Americanism among swaths of the world's population, for whom there is little democracy in the current distribution of global wealth and power. If it turns out that Tuesday's attacks were the work of Osama bin Laden's supporters, the sense that the Americans are once again reaping a dragons' teeth harvest they themselves sowed will be overwhelming.
It was the Americans, after all, who poured resources into the 1980s war against the Soviet-backed regime in Kabul, at a time when girls could go to school and women to work. Bin Laden and his mojahedin were armed and trained by the CIA and MI6, as Afghanistan was turned into a wasteland and its communist leader Najibullah left hanging from a Kabul lamp post with his genitals stuffed in his mouth.
But by then Bin Laden had turned against his American sponsors, while US-sponsored Pakistani intelligence had spawned the grotesque Taliban now protecting him. To punish its wayward Afghan offspring, the US subsequently forced through a sanctions regime which has helped push 4m to the brink of starvation, according to the latest UN figures, while Afghan refugees fan out across the world.
All this must doubtless seem remote to Americans desperately searching the debris of what is expected to be the largest-ever massacre on US soil - as must the killings of yet more Palestinians in the West Bank yesterday, or even the 2m estimated to have died in Congo's wars since the overthrow of the US-backed Mobutu regime. "What could some political thing have to do with blowing up office buildings during working hours?" one bewildered New Yorker asked yesterday.
Already, the Bush administration is assembling an international coalition for an Israeli-style war against terrorism, as if such counter-productive acts of outrage had an existence separate from the social conditions out of which they arise. But for every "terror network" that is rooted out, another will emerge - until the injustices and inequalities that produce them are addressed.