The high kings of history usually ruled over lands of cultural unity; thus high kings differentiate from emperors who control culturally different lands, and feudal monarchs, where subordinates assume lesser positions.
High kings can be chosen by lesser rulers through elections, or be put into power by force through conquest of weaker kingdoms.
In this respect, high kingships frequently differ from empires, which are culturally as well as politically heterogeneous, as well as from feudal monarchies, where the subordinate rulers take lesser titles (such as duke or count) and may be, at least in theory, subject to appointment and dismissal by the sovereign.
The Yang di-Pertuan Agong (literally supreme lord) in Malaysia could probably be seen as a high king, as he is elected from among nine Malay rulers of the states (seven sultans, a raja, and a Yang di-Pertuan Besar-literally great lord) by the Conference of Rulers (through informal agreement, on a rotational basis).
However, after the Mongol Invasions of Korea, these rulers remained technically subordinate to the Mongol Empire and later China until King Gojong declared the Korean Empire in 1897 and assumed the title of Hwangje, or emperor (the Korean rendition of the Chinese 'huang di').