One of the more interesting things when researching online casinos is from where they are based. Like many internet-based businesses, there is no need to be physically located next to resources or even infrastructure. This gives online casinos the freedom to choose in which countries to register based mainly on two criteria.
First, the corporate tax rate and the ease of doing corporate taxes. In the many developed countries, including the USA, it is fairly easy to get a corporate tax rate down into single digits, however, it requires a ton of work, understanding regulation and possibly even lobbying to do it. Meanwhile, there are other countries which you will see mention on the ´about us´ sections of many online casinos such as Panama, Gibraltar, and Malta which offer a very low corporate tax rate, with no struggle required. Every company gets the low tax rate without resorting to loopholes and voodoo accounting. The is probably the main reason why many virtual companies choose to locate themselves based out of these rather obscure places.
It is also an important point that because these countries have gone out of their way to create hospitable environments for virtual companies, and ecosystem of companies are available inside of those companies to help support you there. It is very easy to find support services that a typical virtual company would need.
The other issue is regulation and government oversight. A low tax rate is great, and having a large amount of business available to help you run your business is useful, but not having a government which is intrusive or inconsistent is important. Many of the countries who go out of their way to create very low tax rates for businesses, also know it is important to keep regulations low and consistent. In fact, at times it almost seems like these countries compete against each other to show they are the least overbearing in order to attract companies.
One of the leading locations for online casinos is the small country of Gibraltar, which is off the tip of Spain but is actually part of the UK. Gibraltar is kinda a perfect storm for virtual companies, low tax rates, and because of it´s unusual location and affiliation with the UK, there are very few regulations placed on companies operating out of it.
It is possible this may all change if Brexit actually happens, this would mean there would now be a physical border between Gibraltar and Spain, which might require visas and such to travel back and forth. But also with the UK out of the EU, there could also be more regulations and scrutiny of companies based outside the EU but operating mainly inside the EU. I would expect that if Brexit does come to fruition, that many of the online casinos, especially ones with substantial employee numbers, would move to Malta or Panama.