The term "feudal" has also been applied to non-Western societies in which institutions and attitudes similar to those of medieval Europe are perceived to have prevailed (See Examples of feudalism). Japan has been extensively studied in this regard. Friday notes that in the 21st century historians of Japan rarely invoke feudalism; instead of looking at similarities, specialists attempting comparative analysis concentrate on fundamental differences. Ultimately, critics say, the many ways the term "feudalism" has been used have deprived it of specific meaning, leading some historians and political theorists to reject it as a useful concept for understanding society.