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.

Lets say there's a war in the past which 'A' won and 'B' lost.
And when a person from 'B' meets a person from 'A' it would be really tense.
And you as the character wouldn't know why til you had a trip to the local libiary.

If in the past 'A' and 'B' were friends then something happened to start the war.

It is a good idea to construct a timeline.

10 years ago - 'A' teased 'B'

9 years ago - 'A' reacted to 'B'
7 years ago - 'A' had 'B' surrounded at the final bridge
6 years ago - 'B' signed a treaty to prosime not to mock 'A' about it's inability to wage war
5 years ago - 'C' just formed
1 year ago - 'A' teased 'C'
Present day - 'C' is winning the war

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.