The four qualifications of a state listed in Article 1 of the 1933 Montevideo Convention: a permanent population, a defined territory, a government and the capacity to enter into relations with other states.
In more detail
The criteria are often cited as the customary-law definition of statehood, but in practice recognition by other states is decisive for whether an entity can act as a state. Micronations frequently invoke the criteria to support their claims, yet they usually lack territory not claimed by another state, a stable population or recognition. Artificial structures such as sea platforms are generally not considered territory capable of supporting statehood.