Historians have liberally used emperor and empire anachronistically and out of its Roman and European context to describe any large state from the past or the present. Such pre-Roman titles as Great King or King of Kings, used by the Kings of Persia and others, are often considered as the equivalent. Sometimes this reference has even extended to non-monarchically ruled states and their spheres of influence such as the Athenian Empire of the late 5th century BC, the Angevin Empire of the Plantagenets and the Soviet and American "empires" of the Cold War era. However, such "empires" did not need to be headed by an "emperor". Empire became identified instead with vast territorial holdings rather than the title of its ruler by the mid-18th century.