Using history
The history is important becuase it somewhat says what will happen in the future.
Stereotypes, characters and storylines can be reinforced by it.
If in the past 'A' and 'B' were friends then something happened to start the war.
10 years ago - 'A' teased 'B'
Our character from 'B' is going to help 'A' but our character isn't happy about helping because our character doesn't like 'A'
Remember:- It's your RPG so just make it so you like it, and therefore other people like-you will also like it.