Genetically we seem predisposed to seek links with groups outside our immediate family, and seek differences that distinguish “us” and “them”.  Important in the small groups that early man survived in.
Colour – Western peoples assumed everyone came from Abraham, via Noah, and race/colour were considered mere geographical variations!
Race ideas emerged at same time of slavery – justification?
Idea persists that genetics vary in a significant way between different races – yet we arbitrarily choose to assign significance to genes for skin colour, more than we do to genes for playing the piano!?
Culture – we talk Western civilization, yet this would have been a bizarre concept for most people in Europe for the last 2000 years.  The philosophical and scientific genius of Rome and Greece was lost for a thousand years, and filtered back into Europe via Muslim scholars.
Chicken Tikka has been absorbed into Britishness – now joined by Nando’s!?
Country – Italy and Germany were cobbled together only recently from various city states and duchies.  Scotland is a mix of celtic, gaelic, Scots, highland, lowland, city, country. Nationalism arose during the romantic period, a reaction to rationalism – folk traditions fed into an idea of a national spirit.  The nation state is a project, not an inheritance.  “Cosmopolitan patriotism” – embrace different cultures and identities, in whatever way they appeal or have resonance for you, but choose to live in a particular place, with a particular group.  Use narratives and traditions to create a national identity (but be quick to disown and forget the ugly parts of history) so that when a war comes, people are prepared to defend.  Be proud of what your country has achieved and contributes to the world; be sensitive too, its guilty failings (the difference between patriotism and nationalism).