On 8 September 1951 the Security Treaty Between the United States and Japan was signed. The treaty allowed United States forces stationed in Japan to deal with external aggression against Japan while Japanese ground and maritime forces dealt with internal threats and natural disasters. The United States was permitted to act for the sake of maintaining peace in East Asia and could exert its power on Japanese domestic quarrels. The treaty has lasted longer than any other alliance between two great powers since the Peace of Westphalia treaties in 1648.