Re: Why didn't Chang challenge Gorkon?
If Chang had challenged Gorkon and eventually killed him, the end result might very well have been a civil war. That would have weakened the Empire even further. And when you consider that the Romulans seemed to be in a pretty friendly relationship with the Federation, appearing weak in front of your enemies is not something you want.
Better tactic was to make Federation responsible. An external threat has a funny way to unite a nation against a foreign foe.
"God runs electromagnetics by wave theory on Monday, Wednesday, and Friday,
and the Devil runs them by quantum theory on Tuesday, Thursday, and
-Sir William Bragg