You can't stop conqueror from conquering.
Other than the assassination of course
You will change nothing if enough people still believe a dictatorship would be favourable over their current government.
On a different note, given that christianity was born from the times of disruption following the change in governance in rome, you might also stop a religion like it from forming if you keep rome stable.
You can't stop conqueror from conquering.
Other than the assassination of course
... why do you say that?