Conversation so far:
when was the first clásico of all played
The first meeting of El Clásico was on 13 May 1902.
who is in el clásico
El Clásico is the name given in football to any match between fierce rivals FC Barcelona and Real Madrid.
why is there a rivalry between fc barcelona and real madrid
The rivalry of El Clásico comes about as Madrid and Barcelona are the two largest cities in Spain, and they are sometimes identified with opposing political positions.
what are the political positions that fc barcelona and real madrid are identified with
Real Madrid is viewed as representing Spanish nationalism and FC Barcelona is viewed as representing Catalan nationalism.

Question: how big is the rivalry
Self-contained rewrite: how big is the el clásico rivalry