"Thank you Roma. I will repay you," the 24-year-old told the Corriere dello Sport.
"I am one who never gives up. Anywhere in midfield, I know the idea Zeman has [for the team]. I want to play an important part immediately."
The American was a priority target for the Stadio Olimpico outfit, but his move looked in doubt two weeks ago as Chievo and Roma could not agree on which player to swap for the 24-year-old.
Eventually the two clubs agreed on youngster Adrian Stoian moving to the Flying Donkeys, with the USA international moving the opposite way.
The former Borussia Monchengladbach man has moved to the Giallorossi for 3.5 million euros, and looks to be just one of a number of signings Roma will make this summer.