[Locke Lamora]

This is what I know:
Milan and Inter are both Milanese teams. There's bound to be rivalry.
Moratti is SAD. Berlusconi is funny as hell.

But those things don't entirely justify the almost extreme hatred between the two teams, so I wondered if anyone more educated on the subject than I could answer my questions.

Thanks in advance, Locke.

[Jack Sparrow]

Well if I remember correctly, it's kinda opposite to what I_Ross said. I thought Inter wanted more international players in their side. Hence the name Internazionale. They broke off in 1908.

Also Inter were mostly(then) rightwing, while Milan were predominantly the people's club, being left wing in their political leaning.

Then of course you had all the battles between the ultras. Though to be fair the only worthwhile contest would be between the FDL and the zebras.

Times have changed a lot since then, in fact if anything it's Milan who are more rightwing in nature(their management etc.), but the rivalry still remains.