Gerald Caplan is an Africa scholar, former NDP national director and a regular panelist on CBC's Power and Politics.

There are two main explanations for why some Islamist extremists want to terrorize the western world, each with implications for public policy.

The first was spelled out after 9/11 by U.S. president George W. Bush: "They hate our freedoms: our freedom of religion, our freedom of speech, our freedom to vote and assemble and disagree with each other."

Story continues below advertisement

More recently, Stephen Harper has made the same point. Canadians "are targeted by these terrorists for no other reason than that we are Canadians. They want to harm us because they hate our society and the values it represents."

Presumably, then, we have no choice but to try to wipe them out before they wipe us out. As Mr. Harper put it recently, throwing around pronouns rather loosely, when they "fire at us, we're going to fire back and we're going to kill them."

But both terrorists themselves and those who study them present a dramatically different explanation. Osama bin Laden himself, for example, said the 9/11 attack reflected his deep anger at America's Middle East policies. He was appalled by the hundreds of thousands of Iraqi children who died from lack of food and medicine due to American sanctions and resented the deployment of American forces throughout the Gulf states, particularly in his own homeland, Saudi Arabia. He repeated such sentiments many times.

American authorities did not consider them mere propaganda. Michael Scheur, the CIA's top Middle East specialist, accepted that Mr. bin Laden "has been precise in telling America the reasons he is waging war on us. None of the reasons have anything to do with our freedom, liberty, and democracy, but have everything to do with U.S. policies and actions in the Muslim world."

Canadians were given the same reasons by Michael Zehaf-Bibeau, who murdered Cpl. Nathan Cirillo at the Ottawa War Memorial. In his self-shot video immediately before his rampage, Mr. Zehaf-Bibeau explained that his actions were spurred by Canada's military involvement in Afghanistan and Iraq. He accused Canadians of having forgotten God by occupying Muslim territories and killing righteous people. His attack, he said, was in retaliation for Canada's actions. Did Stephen Harper somehow miss this video or did he simply dismiss its message?

Other experts besides Michael Scheur have long taken such statements seriously. Back in 1997, for example, a U.S. Department of Defense study concluded that "Historical data show a strong correlation between U.S. involvement in international situations and an increase in terrorist attacks against the United States."

The Pentagon spooks didn't have to look far for evidence. The World Trade Centre, it's often forgotten, was first bombed in 1993. One of the perpetrators actually wrote the New York Times stating that the gang was motivated by "deep resentment against U.S. policies in the Middle East," particularly its close ties to Israel.

Story continues below advertisement

Similarly, Eliza Manningham-Buller, former head of Britain's MI5 intelligence agency, reported that "Our involvement in Iraq [since the U.S.-U.K. invasion] radicalized…a whole generation of young people."

Among many examples of those so radicalized was Hussain Osman, who was involved in the deadly bombing of the London subway system in 2005. Captured, Mr. Osman told police that "more than praying, we discussed work, politics, the war in Iraq. We always had new films of the war in Iraq….you could see Iraqi women and children who had been killed by U.S. and U.K. soldiers."

Richard Reid, who tried to ignite a bomb in his shoe on a flight from London to Miami in December 2001, told police that his planned suicide attack was to protest against the U.S. campaign in Afghanistan. Mr. Reid had sent an e-mail to his mother explaining that it was his duty "to help remove the oppressive American forces from the Muslims land."

About 10 months later, an Islamist terrorist group killed 202 foreign tourists in Bali. One of them told police that the bombings were "revenge" for "what Americans have done to Muslims." He said that he wanted to "kill as many Americans as possible" because "America oppresses the Muslims."

That same month on death row in Virginia, Mir Aimal Kasi explained why he had attacked several people outside of CIA headquarters back in 1993, killing two. "What I did was a retaliation against the U.S. government" for American policy in the Middle East and its support of Israel."

Lately the world has been trying to make sense out of the baffling crisis in Yemen. The Guardian's foreign affairs columnist Simon Tisdall explained one aspect last week: "The Houthi rebels who've taken over much of Yemen began as a theological movement committed to peaceful co-existence. The group was radicalized by the 2003 U.S.-led invasion of Iraq."

Story continues below advertisement

As for the Islamic State itself, an analysis just published by the Carnegie Council asserts that the brutal movement is driven by the "humiliation that Muslims have suffered at the hands of foreign powers and local dictators" ever since the First World War. The west's conflict with ISIS, it concludes, "has no military solution."

Are these testimonies and interpretations merely committing sociology? Or are there hard lessons here for Canada and its allies?