A country's visa requirements are usually dictated by economical, socio-political and reciprocal relationships between two countries, that is, the traveler's country and the destination country. A Visa allows the visitor to enter and remain in that country legally for the period of time and purpose stated on the Visa. Visas may be issued for tourism, family visits, business visits, work, medical reasons, journalism, conferences and even permanent residence.
Any sovereign nation has the right to establish it's own Visa requirements and categories of visas. As a traveler, there is no legal right to a visa. They are issued solely at a Consulate or Embassy's discretion and they also reserve the right to ask for more than their normal posted requirements if deemed necessary.