The brothers, who were born and raised in France, had a secular Muslim upbringing before their apparent radicalization. There have, of course, been other attacks on the continent, and thousands of European Muslim extremists have traveled to Iraq and Syria to fight.

　　To find out more about what's leading to the radicalization of many of these young men, I spoke earlier this afternoon to Peter Neumann, director of The International Center for the Study of Radicalization. He's at King's College.

　　Peter Neumann, thank you for talking with us.

　　First of all, what do you think is most important for us to know about this attack, about these two brothers in terms of understanding what went into this, what was behind it?

　　PETER NEUMANN, King's College, London: I think the two brothers are interesting because they had a long history of extremism.

　　At least one of them has been active in jihadist circles for over 10 years. So these were not inexperienced people. These were not people who were the typical lone wolves who were radicalized over the Internet. These were experienced operators.

　　The second important thing is the change of modus operandi that we are witnessing. Really, over the past 10, 15 years, we have been lucky, because the jihadists have been trying to emulate 9/11, very complicated, complex, big attacks. Now they are trying to do less complicated attacks, which they realize can inflict as much horror and terror and polarization on society, but which are much more difficult to detect.

　　I would expect to see more things like that to happen in 2015.

　　JUDY WOODRUFF: Why would you say so many young Muslims in Europe are becoming radicalized?

　　PETER NEUMANN: I think the cause is ultimately a conflict of identity.

　　It is about second- or third-generation descendants of Muslim immigrants no longer feeling at home in their parents or grandparents' culture, at the same time not being fully accepted into European societies, often having experiences of discrimination. They do not feel they belong into France, even though they were born in France, they went to school in France, they have French passports.

　　And I think it is in this regard that we have a lot to learn from the United States of America, which is much more welcoming and much more embracing immigrants, wherever they come from and whoever they are. In Europe, we still have a sense of, you know, if you don't look European, if your names are not European, you're not part of us.

　　And that causes that conflict of identity that makes a lot of people open to the simple messages from radicalizers and recruiters.

　　JUDY WOODRUFF: We also are aware that there's a growing backlash in parts of Europe, including France, against the Muslim population. Is there an understanding of how that may be making the radicalization of these young people worse?

　　PETER NEUMANN: Absolutely.

　　And I think it's a really dangerous moment for a lot of Western European countries. You have a difficult economic situation in countries like France, but also other countries. You have a strengthening far-right fringe. In France, for example, it's not even a fringe. It is now the largest party in France, the Front National.

　　And these people are now trying to exploit, cynically, politically exploit this tragedy to gain strength. And you can almost foresee a situation in which both extremes are almost drawing strength from each other and polarizing society, to the extent that some European countries may become ungovernable.

　　JUDY WOODRUFF: So, what else — what more should governments, should security forces be doing right now to try to head off more attacks like this one?

　　PETER NEUMANN: I think it's very important to, first of all, stop people from traveling to Syria.

　　In a lot of European countries, that's still difficult for legal reasons. You should be able to take away passports from people who want to go to Syria. It is also important that European countries become better at exchanging information. A lot of the returnees are not returning directly — directly to their home countries. They're returning to other companies.

　　So, it's important that everyone knows about each other's returnees. And most importantly is prevention. It is about trying to prevent more people from becoming radicalized in the first place. A lot of countries do not have strategies in place. They do not know what they are doing. And this is absolutely urgent now.

　　JUDY WOODRUFF: Well, so much more to work on this in this area.

　　Peter Neumann with King's College in London, we thank you.

　　PETER NEUMANN: Thank you.