Complex sentence: The competition for a few slots is extremely high among conscripts, because it is widely believed among Koreans that the U.S. Military is less abusive and more professional in its training and treatment of soldiers compared with the ROK Army.
Split into simpler sentences: The competition for a few slots is extremely high among conscripts, because it is widely believed among Koreans that service in the U.S. Military is easier than the Korean Army. Many conscripts also believe that the U.S. military is less abusive and more professional in its training and treatment of soldiers compared with the ROK Army.