What do you mean "not known". You do know that the founders and majority of the forces of the 4 (Rashidun, Umayyad, Abbasid, Fatimid) of the 14 biggest empires in world history came from what is now KSA? Let alone numerous ancient Semitic peoples that migrated from what is now KSA (Arabian Peninsula) and founded empires in the ME way before Islam.
If you are talking about the more modern age then KSA was never been a Western colony, most parts of KSA have never been ruled by outsiders and all the military conflicts KSA has entered since it's founding have been victorious.
Also Saudi Arabians as a people have a warrior past.
If you are referring to experience in numerous wars/prolonged conflicts then you are right. But that's another thing altogether.
Also this is ridiculous. KSA is not invading other countries unless asked. Only Bahrain is a recent example. ISIS? They have no connection to the government of KSA nor would KSA invade Iraq. That's utter ridiculous.
Iran is not going to do it either.