1. Is it an official Nikon USA import or grey market? If the latter, Nikon USA will not honor the warranty (even a so-called 'international' one) and will not service or repair the camera.
2. Even if official USA, is Overstock an authorized Nikon dealer by Nikon USA. (You can find a list of authorized dealers on the Nikon USA Web site.) I'm not sure if, for the warranty to be valid, you have to buy from an authorized dealer. Others here can address that.
3. If 1. and 2. are O.K., the next thing to check is whether the camera ships with everything that Nikon supplies with the body, or whether it is literally 'body only' - i.e., no battery, strap, charger, etc., all of which they would then charge extra for. You can check B&H to see what's normally included in the box.