Ruling system, for example, welcomed by prince after revolution (6)
I believe the answer is:
regime
'ruling system' is the definition.
(I've seen this in another clue)
'example welcomed by prince after revolution' is the wordplay.
'example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'welcomed by' means one lot of letters goes inside another (letters welcomed inside).
'prince' becomes 'emir' (I have seen 'Arab prince ' mean 'emir' so perhaps 'prince' could also mean 'emir').
'after revolution' says the letters should be written backwards.
'emir' in reverse letter order is 'rime'.
'eg' put inside 'rime' is 'REGIME'.
'for' acts as a link.
(Other definitions for regime that I've seen before include "The government in power or systematic plan" , "Dominion of emigre" , "Government - administration" , "co-ordinated programme" , "Authoritarian system" .)