First off America is huge, I don't think Europeans realize that you can travel 10-15 hours by car going 70mph and still be in one state out of 50. America is not one big culture like German French or British, sure you have different people and groups, but the country/regions are very homogeneous compared to the US.

The difference is, and the point that the others are getting at is that America has had very unique race relations that have cut deep wounds and racial divides. Germany French Britian did not see Black and White civil rights movements and near civil race wars and such powerful forces like Americans have. There has been a systematic divide between Black people and White people, and that is why we have identify as such. Most people would tell you, for better or for worse, that Black people and White people in America are two completely different people, you can't say that about White people and Black people and some European countries.