To add to what iGaming Diva said; USA players are essentially limited to just a handful of poker rooms.
There's Bovada Poker, which is basically Bodog re-invented for USA players only (they are on their own network).
There's Aced Poker, Carbon Poker, and PDC Poker. These are all on the Merge Network.
And then there's Lock Poker, which is on the Revolution Gaming Network (formerly the Cake Network).
There are a few other "skins" for the Merge Network and the Revolution Gaming Network that also accept USA players, but we recommend the poker rooms above over all the others.