How are you doing Vu Tran-Thanh,
Have you found a school in the USA where you want to apply? If you have found a graduate study program in the PhD level already, and you are asking whether your previous academic college credits can be applied toward a (PhD Program), the answer to this question is---a sure yes! Most schools in the states work very much the same way---as they are in your neck of the woods---schools accept college credits and will account them toward the degree you want to study. But know this: not all credits from you masters' program will be accepted---even if a school would count all (masters credits) toward the degree you want to pursue---the school would still give you more courses/subjects to take. Though schools differ in requirements, most have a minimum of at least (9 credits) for you to take in their school or in the program---as a requirement to get the degree. If your question pertains to whether or not the schools here in the states would not accept you for---lack of research academic work, the answer is No! PhD programs---has been addressed here already, can be difficult, but not impossible to achieve---we have so many people now with that academic achievement in classrooms, (i.e., educators in colleges and universities, right?). Go ahead and apply and write your statement if the school will ask you for it, but if the school won't ask for an explanation, then, don't worry about it---do not write a Statement of Purpose, in other words. Go ahead and apply and be prepared to have the (tuition money) and the (stamina) to work hard to finish the program. Come back on this teacher's forum and share with us how did you get through the program. We want to hear success stories from colleagues on this platform. Good luck!