During Wei, Jin, Southern and Northern Dynasties, Goguryeo, located in northeast China, began to prosper. Under Northern and Southern Dynasties, Goguryeo had already occupied Liaodong, northern part of Korean Peninsula, and area of the Songhua River. The prosperity of Goguryeo posed a huge threat to western Liaoning. Emperor Sui Yang once "conquered Goryeo three times" but failed. At same time, two regimes arose in southern part of Korean peninsula: Baekje and Silla, among which Baekje and Goguryeo were national regimes established by Fuyu peoples in Northeast China, and Silla were Sanhan peoples. The earliest dynasty in history. However, in Korean history books, Goguryeo, Silla, and Baekje are referred to as "Three Kingdoms Era".
Three Kingdoms of Korean Peninsula
Among Three Kingdoms, Baekje is weakest. To deal with Goguryeo and Silla, Baekje allied with Japan. And Japan is also trying to establish a stronghold on Korean Peninsula. So, Yamato Dynasty of Japan sent troops to Korean Peninsula, invaded Silla, occupied land of Bianhan, and founded "Japan House". Due to strong power of Japan, Baekje also had to be controlled by Japan and pay tribute to Japan. In the early 7th century, Goguryeo power minister Gai Suwen came to power and joined Baekje to attack Silla. Since then, Japan, Goguryeo and Baekje have formed an alliance.
At beginning of founding of Tang Dynasty, envoys were constantly sent to improve relations between countries of Northeast Asia. Of course, it was Goguryeo that posed a direct threat to borders of Tang Dynasty, so Tang Dynasty eventually decided to ally with Silla. In 645, Emperor Taizong of Tang sent troops to conquer Goguryeo, attacked ten cities in Goguryeo, occupied Liaodong Peninsula, and achieved a preliminary victory in Eastern Expedition. In 647, Emperor Taizong of Tang conquered Goguryeo again and Silla also sent troops to cooperate with Tang dynasty, but Baekje took opportunity to attack Silla, inflicting heavy casualties on Silla. The entry of Tang forces into northeast caused an alliance of main forces in northeast, and Mohe and Goguryeo formed an anti-Tang alliance. In 654, allied forces of Goguryeo and Mohe attacked Tang dynasty but failed, so they turned to attack Silla, so Tang dynasty continued to march east and Goguryeo continued to suffer disastrous defeats. In 660, Silla was attacked by Baekje and turned to Tang Dynasty for help. So, Tang Dynasty army crossed Yellow River under leadership of Su Dingfang, directly destroyed Baekche and founded Xiongjin and other five capitals here.
After Baekje was destroyed, its remnants fled to Japan and asked Japan to send troops to intervene. And Japan did not want to sit back and watch Tang Dynasty uproot stronghold on Korean Peninsula, so it decided to send a large army to land on Korean Peninsula. In 663, Japan sent 400 warships to Baijiangkou to land, but they were intercepted by 170 warships from Tang Dynasty and Silla allied forces. The famous Battle of Baijiangkou broke out between two sides. As a result, all 400 Japanese warships were destroyed, army was practically destroyed, and Japanese troops announced their withdrawal from Korean Peninsula. After that, coalition forces of Tang and Silla razed Goguryeo to ground. Since then, Japan has learned lessons, constantly studied culture of Tang Dynasty, and established a centralized system of power, and its social economy has developed rapidly.Second War: The Yuan Dynasty Conquered Japan
In 1206, Mongol Khanate was founded. In next few decades, Mongolia swept across Eurasian continent and became largest country in world at that time. After occupying Liaodong in Kingdom of Jin, Mongolia continued to invade Goryeo dynasty in Korea, forcing Goryeo to surrender. In 1260, Kublai Khan ascended throne of Great Khan of Mongolia in Monan. In 1262, Kublai Khan sent envoys to Japan via North Korea asking for "communion" with Japan, but was rejected by Japan. In 1268, Kublai Khan again sent envoys to Japan, but was still rejected by Japan. Kublai Khan consistently threatened Japan with war. At this time, real power of Japanese shogunate was in hands of powerful minister Hojo, who decided to become an enemy of Yuan dynasty and strengthened defense of Kyushu.
Kublai Khan was very unhappy with Japan's attitude towards Mongol Empire. In 1268, Kublai Khan was ready to start a war against Japan, but gave up because North Korea did not have sufficient military and financial support at time. After Kublai Khan established Yuan Dynasty, he established "Eastern Conquest Province" in North Korea and set up a marshal's mansion at mouth of Heilongjiang River to prepare for an attack on Japan. In 1273, Kublai Khan sent an army to Korea, but North Korea was unable to provide enough supplies, causing army to quickly retreat.
In 1274, Kublai Khan ordered Zhengdong Marshal Xin Du, right and left deputy marshals Hong Chaqiu, and Liu Fuheng to command 20,000 Mongol and Han troops, 5,600 Korean soldiers, and 6,700 sailors. A total of 32,300 people set out from Hepu, Korea to march east. Soon, Yuan Dynasty army landed on island of Kyushu, and Japanese army steadily retreated. However, Yuan Dynasty army did not know how to fight in mountains, so they could not go deep into island of Kyushu. After Liu Fuheng was hit by an arrow, Yuan army retreated to ship. In evening, a typhoon broke out, and 200 warships of Yuan dynasty were destroyed, Xin Du retreated home overnight on remaining ships. The first eastern expedition of Yuan Dynasty failed.
After failure of first eastern expedition of Yuan Dynasty, Kublai Khan sent envoys to Japan, but they were all killed by Japanese. Kublai Khan became very angry and began to prepare for second expedition. In 1279, Yuan Dynasty destroyed Southern Song Dynasty and unified East Asian continent. It was time for second Eastern Expedition. In 1281, Yuan dynasty ordered Fan Wenhu, Li Ting, and others to lead a Han army of 100,000, a Mongol army of 45,000, a Goryeo army of 50,000, and 3,500 warships to march east. The Goryeo army took lead but failed at Tsushima Island and returned. Soon, main forces of Yuan Dynasty captured island of Iki, and then landed in various parts of island of Kyushu. At this time, Japan's combat capability has increased, and Yuan Dynasty army did not take advantage of this, and it still cannot penetrate deep into island of Kyushu. After some battles, Yuan Dynasty troops returned to ships. However, a typhoon broke out again at night, and a large number of Yuan Dynasty ships were destroyed. The second Eastern expedition failed. In 1286, Kublai Khan tried three times to conquer Japan, but surrendered due to outbreak of war with Vietnam.Third War: Wanli Korean War
In 1588, Toyotomi Hideyoshi unified Japan, ending Warring States era. However, due to uneven trust management, domestic conflicts were very acute. To divert internal conflicts and at same time satisfy their own expansionist ambitions. Toyotomi Hideyoshi decided to invade North Korea and then used North Korea as a springboard to attack China. At time, North Korea's internal politics were corrupt and partisan disputes continued, giving Toyotomi Hideyoshi an opportunity. The Ming Dynasty, as overlord of North Korea, had just undergone reform of Zhang Jiuzhen, and its national power was restored and its treasury was sufficient. It can be said that Japan at this time is experiencing most powerful time in last 100 years of Ming Dynasty.
In 1597, Toyotomi Hideyoshi mobilized 140,000 soldiers here and unleashed Second Korean War. The Ming Dynasty also immediately sent Xing Jie, Shangshu of War Ministry, as governor, Yang Gao, Qiandu censor as manager, and Ma Gui as admiral, and entered North Korea for second time. Both sides were sawing in central part of Korea, because of which Japan's plan for a quick victory did not materialize. In 1598, Ming army launched its first large-scale counterattack, but due to Yang Gao's jealousy and unwillingness to share attack with other generals, it eventually failed, and Yang Hao fled in embarrassment. After that, Ming Dynasty dismissed Yang Gao and took over strategy of Wang Shide, governor of Tianjin. After that, Ming army split into four armies for a counterattack, predicting outcome. After that, Toyotomi Hideyoshi died, and Japanese army was shocked, and Ming army stepped up offensive. In end, Japanese army mostly retreated towards Busan. Deng Zilong and North Korean general Yi Sun-sin sent a fleet to lay siege and massacred over 10,000 Japanese soldiers. Japan finally withdrew from Korean Peninsula.