The Mongol empire stretched as far as Eastern Europe and the Middle East to the west, parts of Russia to the north, and China to the south. With a formidable army riding on horseback, lending much speed to the Mongols' conquest of many strong kingdoms and empires, and good military tactics, they were able to subdue a large portion of Asia, perhaps one of the largest empires in history. However, despite the size of the Mongol army, it struggled to conquer the tiny kingdom of Goryeo, the first unified dynasty of the Korean peninsula.
It took them more than 25 years to subjugate the small state, and eight invasions before finally breaking through to the royal family. What had the hermit kingdom done in order to fend off the largest empire at the time?
The Goryeo dynasty of Korea was established in 918, right after the Later Three Kingdoms period. For the next 300 years, Goryeo would experience incursions from the Khitan Liao, out of which they gained valuable insight on how to use the two-pronged strategy of the quill and the sword - diplomacy and military prowess - to successfully resist the 100,000-strong Khitan army.
So, when the Mongols came knocking on Goryeo's door, the Koreans did not go down without a fight. Now, by the first invasion in 1231, the Goryeo dynasty was still under the military aristocracy who had fortified the kingdom's defenses with well-trained soldiers. This was further bolstered by wise diplomatic withdrawals and peace negotiations to bide them time to prepare for the next attack.
The dynasty continued on with this quill-and-sword strategy until their dictator suddenly died thus weakening the control of the military aristocracy. Add to this the fact that the Mongols burned fields whenever they were able to subdue villages, Goryeo's royal family would later sue for peace and make an alliance with the Mongols.
(Image credit: History Maps)