U.S. Secretary of State visits Korea

U.S. Secretary of State Rex Tillerson arrives for an official visit to Korea at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued commitment to the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

U.S. Secretary of State Rex Tillerson arrives for an official visit to Korea at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued commitment to the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

U.S. Secretary of State Rex Tillerson speaks with Marc Knapper, the Charge d'Affaires at the U.S. Embassy in Seoul, at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued commitment to the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

U.S. Secretary of State Rex Tillerson speaks with Marc Knapper, the Charge d'Affaires at the U.S. Embassy in Seoul, at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued commitment to the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

Marc Knapper, left, the Charge d'Affaires at the U.S. Embassy in Seoul, U.S. Secretary of State Rex Tillerson, and U.S. Army Gen. Vincent K. Brooks, United States Forces Korea commander, prepare to depart for an official visit to Seoul from Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued strong support of the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

Marc Knapper, left, the Charge d'Affaires at the U.S. Embassy in Seoul, U.S. Secretary of State Rex Tillerson, and U.S. Army Gen. Vincent K. Brooks, United States Forces Korea commander, prepare to depart for an official visit to Seoul from Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued strong support of the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

U.S. Secretary of State Rex Tillerson greets U.S. Army Gen. Vincent K. Brooks, United States Forces Korea commander, at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued strong support of the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

U.S. Secretary of State Rex Tillerson greets U.S. Army Gen. Vincent K. Brooks, United States Forces Korea commander, at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued strong support of the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)

OSAN AIR BASE, Republic of Korea -- U.S. Secretary of State Rex Tillerson arrives for an official visit to Korea at Osan Air Base, Republic of Korea, March 17, 2017. Korea is one of three countries Tillerson is visiting during his first trip to the Pacific region as secretary of state, reiterating the United States' continued commitment to the U.S. - Korean alliance. (U.S. Air Force photo by Staff Sgt. Victor J. Caputo)