Normally in the FAA system you get a private followed by a commercial and then the ATP. One of the requirements for a FAA commercial is to hold a FAA private. (US military pilots or foreign military pilots attached to a US military unit can skip the private.) To get the FAA ATP you must hold either a FAA commercial with an IR or a foreign commercial with an IR or a foreign ATP (again US military pilots have a work around.) No matter which of the three ways you qualify, the actual path is the same. ATP CTP class before the written, enough flight training to pass the checkride and the checkride. Holding a foreign license just allows you to skip getting the lower level FAA certificates.