A monarchy is a form of government in which a group, generally a group of people comprising a dynasty, embodies the country's national identity and its head, the monarch, exercises the role of sovereign. The power of the monarch may vary from purely symbolic (crowned republic), to partial and restricted (constitutional monarchy), to completely autocratic (absolute monarchy). In most cases the monarch's position is inherited and lasts until death or abdication. In contrast, elective monarchies require the monarch to be elected.[1] Both types have further variations as there are widely divergent structures and traditions defining monarchy. For example, in some elected monarchies family history is the only criterion for eligibility to be monarch, whereas many hereditary monarchies impose requirements regarding the religion, age, gender, or mental capacity. Occasionally this can result in more than one rival claimants, whose legitimacy is subject to election. There have been cases where the term of a monarch's reign either is fixed in years or continues until certain conditions are satisfied: an invasion being repulsed, for instance.