Anyone have advice for cats fighting suddenly?

Fort Lauderdale FL

Description

I have 2 male, fixed cats (2 and 3 yrs old) that have started fighting suddenly. Mostly the older kitty attacking the younger one. The younger is twice the size of him and not aggressive at all. Just runs away, but I think my older one got in a fight w a stray and is now traumatized and taking it out on the other cat. Anyone know what to do in this situation?