I'm trying to have a healthy discussion with a friend, and we are not clear on the difference between a khan (like Genghis or Kublai) and a king. My friend keeps arguing that Kublai is a king because he is referred to as a "king" by some historian (apparently), but my understanding is that the title of Khan is supposed to be more like an emperor or king of kings (after all, its called the mongol empire, not mongol kingdom).
The discussion seems to boil down to defining emperor vs king, I guess.
If Kublai is an emperor, am I supposed to interpret that literally as "king of kings"? Were there other "kings" (what would they be called?) throughout his mongol empire that just had to answer to Kublai, but really they kinda ruled over their own local kingdom, area semi-autonomously, or did Kublai actually govern as the sole head over the whole empire? If the previous scenario was the case, did Kublai serve as a "king" governing his own local area?
Internet searching points me to ideas about whether an area is conquered via military or if born into ruling that determines king vs emperor. Kublai is clearly born into some ruling power, but he also conquers some new land like China and whatnot, so that doesn't make this easier.
Khan is a very generic title in several languages; individual nomadic tribes had their own khans when they weren't united into confederations by particularly charismatic and successful leaders like Temujin or Nurhaci. Furthermore, the official Mongol title of Genghis and his seniormost successors was 'Khagan', not Khan. Furthermore, numerous Chinese emperors predating the Mongols claimed the title Khan in reference to their central Asian territories, while taking tribute from numerous khans on the northern border. However, after the Mongol Empire, only descendants of Temujin could declare themselves Khan; Timur was certainly as militarily successful and politically powerful as any Khan, but stuck with the title of Amir, since he lacked the proper lineage.
It's very difficult to provide direct equivalents to Western titles (which were often just as ambiguous); one might call a Khan a chieftain or a prince or a king or an emperor depending on their holdings, though Khagan seems to be restricted to those that could claim superiority over other Khans.
The use of the term 'Emperor' in European context is also very idiosyncratic; it originated as a title bestowed on a Roman general by the acclamation of his soldiers, but became the title of the head of state, and was for centuries used only by states that believed themselves official successors to the Roman Empire: the Byzantines, the Holy Roman Emperors, the Ottomans, and the Tsars of Muscovy. It becomes the term for the biggest, baddest states on the block with Napoleon, who was appointed with the title of Consul first, then declared by plebiscite Emperor of the French. After losing the connection with Rome with the dissolution of the Holy Roman Empire, the Habsburgs don't want to step down their titles, so they turn their lands into the Austrian Empire. The Germans make their head of state an Emperor because they didn't want to demote the various subordinate kings, and the British make their queen Empress of India so she's not outranked by the Germans.
In the Chinese context, for centuries, the highest political title ever claimed by a living person was Wang, which is usually translated as 'King'. However, after conquering China, Ying Zheng, then Qinwang, decided he needed a title clearly superior to his rivals and predecessors, so he combined the characters for mythical demi gods Huang and culture heroes Di into the title Huangdi. The context in which European rulers called themselves emperor does not apply in the slightest here, but Emperor is the near universal translation of Huangdi (as well as Huang and Di, just to make things perfectly confusing).
TL;DR, don't get too hung up over translating indigenous titles when the parallels are unclear.