There aren't any international laws about it in Antarctica. There are probably other countries in places like Africa that don't have any laws against it either.

Running a home casino is illegal in most areas because it is too easy for you to rip people off and to go out of business without being able to cover your wages.

But, offshore betting is done all the time and all those gambling websites. Most of them are private operations and started in somebody's home. Since they are set up in third world nations that don't have any laws against internet gambling they are legal and the US can't stop them.

What the US has done to control them is to make it illegal for any bank that does business in the US to process transactions with these companies. It won't stop the off shore betting, but it will stop them from getting hold of your credit card and sucking you dry.