Peter Bergen

The sitting prime minister, Jose Aznar, who had strongly backed the U.S.-led Iraq War, was unseated by a challenger who then pulled Spanish troops out of Iraq. The Madrid terrorist attacks are generally regarded as being the key to why Aznar, who had been leading in the polls, was defeated.

Abu Musab al-Suri is someone I got to know pretty well because he's a Syrian. Very bright guy, lived in London. He actually was the person who took myself and correspondent Peter Arnett and the cameraman, Peter Juvenal, to interview bin Laden for his first TV interview.

Trump has long said he favors a 'safe zone' in Syria to prevent Basher al Assad's regime from carrying out indiscriminate airstrikes against Syrian civilians and to halt the refugee flow out of Syria.

When Abu Zubaydah was shown a series of photos of al Qaeda members by Soufan, he identified one of them as the operational commander of 9/11, Khalid Sheikh Mohammed.

President-elect Donald Trump has a host of national security challenges to deal with as he assumes office, from the resurgence of the Taliban in Afghanistan to the grinding Syrian civil war to the flexing of Russian muscles under President Vladimir Putin to how to deal with ISIS as the terrorist army retreats in Iraq.

Certain Gulf Arabs support proxy jihadist Sunni groups such as al Qaeda's affiliate in Syria, while Iran supports Shia militant forces such as Hezbollah.

On the campaign trail, candidate Trump occasionally raised the idea of creating 'safe zones' for Syrian civilians.

The commonly accepted definition of terrorism is that it is politically motivated violence directed at civilians by entities other than a state. These kind of attacks can come from the far right, the far left, racists of every stripe, as well as jihadists.

Because Scotland and Northern Ireland want to remain part of the E.U., there is the quite real possibility that Scotland and even Northern Ireland might now choose to go their own way on membership within the E.U. and the 'United Kingdom' would suddenly effectively be only England and Wales.

Bin Laden studied economics and public administration before he turned to a life of jihad.

Pakistan's key leaders have succumbed to the assassin's bullet or bomb or the hangman's noose, and the country has seen four military coups since its birth in 1947. Yet the Pakistani polity has limped on.

The dangers of TATP bombs can be seen in the case of Matthew Rugo and Curtis Jetton, 21-year-old roommates in Texas City, Texas. They didn't have any bomb-making training and were manufacturing explosives in 2006 from concentrated bleach when their concoction blew up, killing Rugo and injuring Jetton.

Will there be a political backlash against British Prime Minister Theresa May, whose ruling Conservative Party is traditionally seen as 'stronger' on terrorism than its main rival, the Labour Party?

Abedi appears to be one of the many thousands of Western Muslims who have embraced militant Islam, often as a way of trying to resolve the tension between their split identities.

Apostasy is a grave crime in Islam and punishable by death in the eyes of members of al Qaeda.

Sheikh Rahman had a doctorate in Islamic jurisprudence from al-Azhar University in Cairo, the Harvard of Islamic thought. He also had a long history of guiding terrorist groups.

Al-Qaeda, which means 'the base' in English, lost its base and training camps in Afghanistan, while its leaders were on the run, captured, or dead. One year after the 9/11 attacks, al-Qaeda was still on life support.

In picking Gen. Jim Mattis for Defense secretary, President-elect Donald Trump has said that he found his 'Gen. George Patton.' Yet that label may not really capture what makes Mattis a distinctive choice.

Bush administration officials, of course, deny that they didn't take the threat urgently enough, but there is no debating that in their public utterances, private meetings, and actions, the al Qaeda threat barely registered.

Anne Richard, a senior U.S. State Department official, testified at a Senate Homeland Security Committee hearing in November 2015 that any Syrian refugee trying to get into the United States is scrutinized by officials from the National Counterterrorism Center, FBI, Department of Homeland Security, State Department and Pentagon.