I think it is normally legal unless the country in question explicitly sets out a law to make it illegal.
Absolutely it depends. For the countries who are liberal somehow they doesnt ban gambling and allot public places to their citizen for making casinos there. But as far as some Asian or Middle East countries are concerned, I think for their religion gambling is banned there. Strict punishments have been observed for the individuals who get into this world. Yeah, it differs geographically.