Casino Splendido is regulated by Malta and powered by Microgaming casino games. Both Malta and Microgaming do not accept citizens from the United States of America.
I sent an email to the Casino Splendido support to get a clear explanation. Here is their answer :
Thank you for your email. We do not currently offer any services to the USA. However you are permitted to play from any one of the other countries we support shuold you have residence in that country.
We are here for you 24 hours, 7 days a week.
As part of the US gambling law, Casino Splendido preferred to step back from the US Markets. However, some online casinos still continue to accept US citizens. Check our top 3 US Casinos.
Technically, you could play to Casino Splendido if you signed up from abroad. For instance if you are in vacation in Thailand or in Indonesia, you could play to Casino Splendido while you drink your White Russian. However, you should not use a US address and an american credit card (from Citibank for instance).
This is the same problem as "signing-up from abroad". You could use a VPN to play to Casino Splendido, but you would need to have a real address outside of the US (with phone bill at your name for instance). If you have a relative abroad, for instance in the Ireland, it could work. Otherwise, in case you win a $2,000,000 jackpot, Casino Splendido could block your funds..
We know that Bovada is currently accepting US citizens. It is powered by Top Game software and offers a nice welcome bonus.