understanding problem

[dzpqkl]

I've read this in New Concept English:
"Even if one didn't konw from concrete examples(the 1936 Olympic Games, for instance) that international sporting contests lead to orgies of hatred, one could deduce it from general principles"
I want to find out:
1, What had happened during or after the 1936 Olympic Games? Does the author refer to the World War II? As far as I know that war was not caused by sports.
2, What does "orgies of hatred" mean? Is this a metaphor?
3, Does "general principle" mean "common sense"?

Thanks for your attention!

[Tdol]

They were held in Germany, then under Nazi rule, there was a controversial film made of them by Leni Riefenstahl, there were some issues with some African American athletes- Hitler left just before one was presented a medal, etc and he didn't shake hands with Jesse Owens. 'Orgies of hatred' may be overstating things, but I presume they mean that nationalist feeling can run high during such international sporting events.