Joseon Army
The Joseon Army was the army of the Korean dynasty of Joseon. The army defended the northern borders but seldom defended the southern regions. The army was best known for fending off the Jurchen raids and conquering the Korean Peninsula. However, Joseon's neo-Confucianism disavowed military development, causing them to be vulnerable to Japanese and Manchu invasions. Despite this, Joseon kept strengthening the army until the 19th century, when western powers and the Japanese forced them to open doors and modernize the army.
History
Early period
The armed forces of the former Goryeo kingdom were Joseon's armed forces during the reign of King Taejo. However, the officials of the Joseon court commanded private armies from the previous kingdom. Yi Bang-won and his officers staged a coup against Taejo and his brother Jeongjong of Joseon, inciting the first and second strife of the princes. He advised Jeongjong to ban the ownership of private armies and become king in favor of having a central army. When Sejong ascended the throne, he created various military regulations to strengthen the safety of his kingdom, supported the advancement of Korean military technology, including the development of the cannon, mortars, fire arrows and the use of gunpowder.Joseon–Jurchen border conflicts
Like Goryeo, Joseon made the Jurchens in the area around Hamhung on the northeastern Korean peninsula submit as vassals. The Joseon Koreans tried to deal with the military threat posed by the Jurchens by using both forceful means and incentives and by launching military attacks. At the same time, they tried to appease them with titles and degrees, traded with them and sought to acculturate them by having Korean women marry Jurchens and integrating them into Korean culture. Despite these measures, fighting continued between the Jurchen and the Koreans. The Ming Yongle Emperor was determined to wrest the Jurchens out of Korean influence and have China dominate them instead. Korea tried to persuade Jurchen leader Mentemu to reject the Ming overtures, but were unsuccessful since Möngke Temür folded and submitted to the Ming. In 1433, Sejong sent Kim Chongsŏ, a prominent general, north to destroy the Jurchens. Kim's military campaign engaged the Jurchen clans such as the Odoli, Maolian and Udige capturing several castles, taking control of Hamgyong and continued pushing north expanding Korean territory to the Songhua River. He then established 4 counties, 6 garrisons, and several border forts in the region to safeguard the people from the Jurchens shaping the modern borders of Korea around 1450.Oei Invasion
In 1419, King Sejong sent Yi Chongmu to raid the Japanese on Tsushima Island in the Oei Invasion as a response to Japanese Wokou raids on Korean coastal cities. Yi took 227 Korean ships and approximately 17,000 soldiers, landed, attacked, and plundered Japanese pirate settlements on Tsushima Island. The So clan, the ruling family of Tsushima, requested negotiations. In the diplomatic exchanges that followed, Korea permitted the So clan to continue trade with Korean coastal harbors under the condition that the clan suppresses the activities of Japanese pirates.Yi Si-ae's Rebellion
When King Sejo came to power he strengthened the monarchy established by King Taejong by weakening the power of the State Council and bringing staff directly under the king's control. He also strengthened the administrative system to enable the government to determine exact population numbers and to mobilize troops effectively but caused Yi Si-ae's Rebellion. Yi Si-ae led the Iksok Force and the rebel army killing officials from the central government for not appointing northern officials to govern the northern provinces until they were defeated soon after the Battle of Manryeong.Japanese Invasions of Korea
By the 16th century, the military became weak by the disavowment from Confucian scholars. During the Imjin War, Joseon mobilized few military units within a standing army. Its defense depended heavily on the mobilization of the citizen soldiers in case of emergency. When Japan invaded Korea, Joseon deployed a total of 84,500 regular troops. During the first invasion, the Joseon army was no match for their sheer numbers armed with arquebuses and a combination of arms, and the Japanese pushed them north to Pyongyang. When the navy, and the Righteous Army cut off supply lines, this gave the regular army a chance to force the Japanese back to Pusan through many strategic battles. During the 1595–1596 Truce, Seonjo realized how important it was and tried to reform it with the help of Ming generals and established army training centers. Yu Sŏngnyong, the Chief State Councillor, spoke out about the Korean disadvantages. He examined why the Japanese had quickly overrun them and pointed out the flaws of their defense systems. Yu also pointed out how efficient the Japanese army was since it took them only one month to get Hanseong and how well organized they were. He noted how the Japanese moved their units in complex maneuvers, often weakening their enemy with arquebuses, then attacking with melee weapons. These reforms helped Joseon Army repel the second invasion of the Japanese army and win the war.Yi Gwal's Rebellion
After the Injo Coup, the dissatisfied Yi Kwal who helped Injo ascend to the throne incited a rebellion against him for trying to arrest his son, Yi Chŏn. He led 10,000 of his soldiers to occupy Hanseong and replace him with Heungangun, his royal relative as king. But the Joseon army led by General retook the capital and crushed the rebellion. Yi Kwal's Rebellion weakened the military, making them vulnerable to Later Jin's attack.Manchu-Joseon conflicts
Conservative Westerners took hard-line policy toward the Jurchen-led Later Jin dynasty, keeping their alliance with the Ming dynasty. The Later Jin, who had remained primarily friendly to Joseon, began to regard Joseon as an enemy. Han Yun, who participated in the rebellion of Yi Kwal, fled to Manchuria and urged the Later Jin ruler Nurhaci to attack Joseon; thus, the friendly relationship between the Later Jin and Joseon ended.Battle of Sarhū
In 1619, the Joseon Expeditionary Force led Commander Gang Hong-rip to engage Later Jin with the Ming Army at the Battle of Sarhū. But the allied forces lost two-thirds of the Joseon Expeditionary Force. The Jurchen released the captives and allowed them to return to their homeland. Gang Hong-rip, however, was kept for his proficiency in the Jurchen language. Later on, General Gang would be led to believe that his family had died in the political turmoil during a coup in his native kingdom of Joseon. To exact his revenge on the Joseon court, he urged Jin to invade Joseon, which led to the First Manchu invasion of Korea in 1627. Only during the peace negotiations did he find out that he had been misled.The Joseon musketeers being overwhelmed by the Manchu cavalry prompted a revision of military tactics in Korea. In previous decades, the Imjin War was seen as a demonstration of the dominance of the firearm, and Joseon adjusted military forces accordingly. Both sides of the war lacked effective shock cavalry to take advantage of the vulnerabilities of unsupported musketeers. After the defeat at Sarhū, the Joseon forces revised their doctrine to have spearmen supporting the musketeers.