I disagree on that, dustie.
It might be generic sometimes, but its almost coded and a part of the reactionary "brotherhood" which exists in Islam that a Muslim would stand up for another Muslim. This especially happens when a Non-Muslim is involved (or a Muslim from another sect).
Sure, I realise that, even I've been told to see fellow muslims as brother/sisters, but similarly you have nationalism and even racism, it's more like the title suggests a tendency for tribal mentality and I think it comes from the 'safety in numbers' and finding some common ground. So in that sense sure islam asks for it but fundamentally it's a general trait seen in all places and levels. Not that it can't be changed, changes make us progress of course, least they should do