Today, both North Korea and South Korea field some of the largest and most lethal armies in the world. On one hand, North Korea is widely suspected of having nuclear weapons, as well as other weapons of mass destruction. South Korea, for its part, is equipped with a sophisticated conventional military with state-of-the-art weapons. In addition, South Korean troops actively participated in the Vietnam War, contributing the second largest foreign military contingent after the United States, and are currently serving in various UN peacekeeping missions around the world. The South Korean military enjoys military alliances with other countries, particularly the United States.
^Miller, Owen (2014). Korean History in Maps. Cambridge University Press. p. 29. ISBN978-1107098466. Retrieved 25 June 2016. "After the Tang dynasty succeeded the Sui, the second Tang emperor also tried to bring Goguryeo under its control, launching an unsuccessful attack in 645. Goguryeo repelled a second invasion in 662 with victories by the general Yeon Gaesomun."
^Kim, Djun Kil (May 30, 2014). The History of Korea, 2nd Edition. ABC-CLIO. p. 66. ISBN978-1610695824. "Later, in 1018, however, a third large-scale invasion from the Khitan was thwarted by Goryeo forces led by the general Gang Gamchan (948-1031). The Khitan thereafter gave up trying to subjugate Goryeo by force."
^Lee, Ki-Baik (1984). A New History of Korea. Cambridge, Massachusetts: Harvard University Press. p. 165. ISBN978-0674615762. "Yi Sŏng-gye himself won advancement through his success in the numerous battles of his day. He played a major role in repulsing the attacks of the Red Turban bandits and Japanese marauders, as well as in the campaign against the Yüan Tung-ning Commandery in Manchuria."
^Lee, Hyun-hee; Park, Sung-soo; Yoon, Nae-hyun (2005). New History of Korea. Jimoondang. pp. 199–202. ISBN9788988095850.
^Shin, Hyoung Sik (March 31, 2005). A Brief History of Korea. Seoul, Korea: Ewha Womans University Press. pp. 29–30. ISBN978-8973006199.
^Lee, Ki-Baik (1984). A New History of Korea. Cambridge, Massachusetts: Harvard University Press. p. 37. ISBN978-0674615762. "Then, in 371, Paekche struck northward into the Koguryŏ domain as far as Pyŏngyang, killing the Koguryŏ king, Kogugwŏn, in the course of the campaign. Paekche thus came to hold sway over a sizeable portion of the Korean Peninsula, including all the modern provinces of Kyŏnggi, Ch'ungch'ŏng, and Chŏlla, as well as parts of Hwanghae and Kangwŏn. Furthermore, King Kŭn Ch'ogo solidified his international position by making overtures to the Eastern Chin state in the Yangtze river region and to the Wa people in Japan."
^Graff, David A. (2002). Medieval Chinese Warfare, 300-900. London: Routledge. p. 201. ISBN9780415239554. "In 674 and 675 Tang forces under Liu Rengui attacked Silla itself. Chinese histories record that Liu was victorious and forced the king of Silla to sue for peace, while Korean historians report the defeat of the Chinese armies. The fact that the Tang government found it necessary to withdraw the headquarters of its Korean protectorate to the Liao River valley in the early months of 676 suggests that the Korean version is probably closer to the truth. Silla was left in uncontested control of almost the whole of the Korean peninsula, and there was no great Tang campaign to recover what had been won with such difficulty and so quickly lost."
^Choi, Wan Gee (2006). The Traditional Ships of Korea. Ewha Womans University Press. pp. 66–67. ISBN978-8973006830. Retrieved 25 June 2016. "Using his official position and his immense military influence, Jang Bo-go amassed substantial wealth by controlling maritime trade between Silla, Tang and Japan. The famous American scholar of Asian history, Edwin O. Reischauer hailed Jang Bo-go as the trade prince of the maritime commerce empire. As Jang emerged as a formidable force in the sea, high-ranking officials in the Silla capital, Gyeongju, could no longer ignore him. Jang Bo-go ruled his domain with absolute political, military and economic autonomy."