The concept of a unified white race did not achieve universal acceptance in Europe when it first came into use in the 17th century, or in the centuries afterward. Nazi Germany regarded some European peoples such as Slavs as racially distinct from themselves. Prior to the modern age, no European peoples regarded themselves as "white", but rather defined their race, ancestry, or ethnicity in terms of their nationality. Moreover, there is no accepted standard for determining the geographic barrier between white and non-white people. Contemporary anthropologists and other scientists, while recognizing the reality of biological variation between different human populations, regard the concept of a unified, distinguishable "white race" as socially constructed. As a group with several different potential boundaries, it is an example of a fuzzy concept.