India is mindbogglingly diverse. Each village is very different from the next one, yet they look all the same. One has to live India to really understand the diversity of our social fabric and yet, we stand as ONE nation. If you compare other societies/countries with India, you will truly understand how really diverse India is and how true - "Unity in Diversity" actually is.
Its not only wars that unites us, there are many issues on which Indians stand shoulder to shoulder. We have our differences and the attempts made to resolve those gets our undivided attention creating an illusion of discontent. We have our regional identities and yet we value our national identity.
Let me give an example. When I first joined the University here in US, we had a semi-formal introduction to the faculty. All students introduced themselves with their names and countries of origin. Nothing else. Indians, not only stated their names, but their cities/region/state and then followed by - India. That should pretty much sum up how we view ourselves.
On a lighter note, you forget Cricket - the undisputed supreme religion of the subcontinent - especially India.