Following the Armistice, South Korea and the U.S. agreed to a "Mutual Defense Treaty", under which an attack on either party in the Pacific area would summon a response from both. In 1967, South Korea obliged the mutual defense treaty, by sending a large combat troop contingent to support the United States in the Vietnam War. The US has over 23,000 troops stationed in South Korea, including the U.S. Eighth Army, Seventh Air Force, and U.S. Naval Forces Korea. The two nations have strong economic, diplomatic, and military ties, although they have at times disagreed with regard to policies towards North Korea, and with regard to some of South Korea's industrial activities that involve usage of rocket or nuclear technology. There had also been strong anti-American sentiment during certain periods, which has largely moderated in the modern day.