We all know the scene where Simba and Zira interrupt the cubs (Kovu and Kiaras) play. Zira seems oddly excited to see Simba, and he appears angry. However, when Zira notices Nala, her reaction is completly different, and Nala gives the older lioness a look of pure contempt. What do you suppose is the backstory there?
Just throwing a theory out there: As we know, Zira believes that Simba killed Scar. A theory: Zira, stricken with grief, attacks Simba and tries to kill him. (This might be how she got her scar) Nala, along with the other lionesses, defends her mate. Perhaps some other lionesses tried to defend Zira too, and they all got banished for this.
Also, the line about the Outlanders being murderous and backstabbing.. "You can`t turn your back on them." - Seems to me they`re referring to something pretty serious.