From a historical point of view, an emirate is a political-religious unit smaller than a caliphate.
A great number of previously independent emirates around the world are now part of larger states, as can be seen in Nigeria.
[3] Etymologically, emirate or amirate (Arabic: إمارة imārah, plural: إمارات imārāt) is the quality, dignity, office, or territorial competence of any emir (prince, commander, governor, etc.).
As most emirates have either disappeared, been integrated in a larger modern state, or changed their rulers' styles, e.g. to malik (Arabic for "king") or sultan, such true emirate-states have become rare.
They are arranged by location and in order of the date of the first leader styled "emir."