One common link between many young extremists is the search for a commanding figure in their lives -- a figure that embues their lives with some dignity and meaning.

An excerpt:

In a study of 3,000 Palestinian children in Gaza — where the militant Hamas and Islamic Jihad groups attract young people ready to die for their cause — psychiatrist Eyad al Sarraj discovered that nearly half of them had seen their fathers humiliated or under violent attack by Israeli forces.

"(In their view) the father is helpless, impotent and unable to protect himself," Sarraj says. "Comes the time when they are teenagers, a father replacement comes into the group. Hamas, or Islamic Jihad, which takes the role of the father, takes them in."

Through the radical Islamic groups, Sarraj says, "they identify with the ultimate figure: God. Why God? Because in contrast to the original father, God cannot be humiliated. He can only be (a figure of) dignity. God can only be victorious. If you die for God, you don't really die."

Many potential suicide bombers in other countries come from homes that are not threatened with violence. And, points out psychiatrist Jerrold Post, "there is a real distinction between the Hamas recruits and the suicidal hijackers of 9/11, who come from comfortable upper middle-class homes."

Some of the Al Qaeda recruits, like those who carried out this month's London attacks, were older than the schoolboys flocking to join Palestinian militants, he says. But they were also seeking a form of authority.

"On the whole, I see them as fully formed adults. But they are similar to cult members, because they submerged their personalities in those of their leader," said Post, director of the political psychology program at George Washington University.

Most of the London bombers identified so far belong to the second generation of immigrant communities that have struggled to survive and find a place in a new country.

"That has caused an adolescent loss of identity, and a search for some kind of stability," says terrorism expert Ronald Crelinsten, a Europe-based senior research associate of University of Victoria's Centre for Global Research. "They don't find it in their parents. They turn to an authority figure, somebody who tells them things are black and white."

And, he says, "if you're alienated from your own parents, you don't respect their values, and if you're looking for meaning, you can easily find an alternative in the seductive authority of a cult-like group."