Some nations (e.g., Mexico) require a specific amount of military service from every citizen, except for special cases, such as physical or mental disorders or religious belief. Most countries that use conscription systems only conscript men; a few countries also conscript women. For example, Norway, Sweden, North Korea, Israel, and Eritrea conscript both men and women. However, only Norway and Sweden have a gender-neutral conscription system, where men and women are conscripted and serve on equal formal terms. Some nations with conscription systems do not enforce them.