Now we can see what has happened in Paris with theirs opened multicultural country. There are a lot of blacks and muslims inside. I`m not against blacks and muslim, I`m against radicals in general. Nevermind. What can we do to prevent similar cases in the US? This question rises because we cannot completely rely on the government
Paris has always been multicultural. Partly because it's a European cultural centre, partly because it has a colonial past.
When I lived there 35 years ago I hung with North Africans all the time. I could describe them as "Muslims" since they probably were in the same sense that I would be called "Catholic" in that it was what we grew up in, but our relationships had nothing to do with either.
The city was teeming with Arabic, German, English, Italian, lots of African indigenous languages, Asians anything you can think of, and it wasn't new then. It gave (and gives) it the vibrancy and vitality it's known for.
And it's in no way anything new, or unique to Paris.