The 20-year-old will join the Potters on January 1, 2014 when his contract with New England Revolution expires.
Stoke manager Mark Hughes said: "We've put a lot of work into this deal, and I am delighted that we have managed to get the deal over the line.
"It's a good deal for us because he is a very good young player who boasts a lot of talent, as well as a lot of potential too.
"I've known of him for a couple of years now. He burst on to the scene for the United States at the age of 17 and everybody has paid attention to him since.
"I have kept my eye on him for the last 18 months, and thankfully we were in a position where we were able to pull this deal off."
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