I think this goes way deeper than the Charlie Hebdo attacks.
And it's an incredibly complex problem that is not going to go away easily, if at all. And it's also not just in France. We're seeing the same problems here in Sweden, and most likely all over Europe.
Immigrants from Africa and elsewhere are coming to Europe in search of a better life and a future, but what they find is in many cases unemployment and new hardships. I can mostly just speak for how it is here of course, but our society just hasn't been able to cope with all these people. There are not enough jobs to go around, and during the great migration crisis a few years ago things got so bad that we didn't even have somewhere to house all the people coming here. We're still struggling with the effects of that period.
Add to this the major cultural differences that exists and you have a recipe for disaster.
This is just scratching the surface of course. There are so many aspects to this problem... sociological, religious, cultural, economical, and yes even racial. Racism has always been a part of European society and the horrors of WWII and the nazis are not as prominent in people's minds anymore. It's just 75 years since the war ended and you're already hearing a lot of rhetoric similar to what you'd hear in the 1930s.