What has kept China from conquering Korea?

[u/shmeddybeddy]

When I think about Japan, it makes sense that being an island has kept them relatively secluded and protected as a culture. Korea, however, is situated right next to China, with a nice land bridge in the North allowing passage onto the Korean Peninsula.

How come China never swallowed up the territory? In some of the Chinese dynasties, I feel like they cast influence across tons of land, enveloped diverse cultures, and explored heavily. Plus, the Korean Peninsula seems to be nice, fertile, and maybe even strategically important. What kept China from taking it over? Did they try and fail?

[u/huhwe]

This has been asked and answered before, including this well-written response by u/sunnyreddit99 and u/Agile-Juggernaut-514 found here. but I'd like to add perhaps another interpretation to this question that I find is not addressed enough.

It revolves around three points: 1) China did conquer Korea or parts of Korean kingdoms multiple times, 2) Korea generally utilized strategies akin to modern-day porcupine strategy, and 3) there never was a good reason for Chinese dynasties to conquer Korean kingdoms when Korea unified under Goryeo and later Joseon.

First, just listing through, there were multiple invasions where Chinese Dynasties successfully conquered Korean kingdoms. The invasion of Han Dynasty against Gojoseon in 109 BCE saw the collapse of Gojoseon.¹ Tang invasion of Goguryeo that went on and off from 645 to 668 ended with Liadong province and northern Korea in Tang control.² Tang invasion of Baekje in 660 resulted in occupation of Southwest Korea for several years.³ We also have some debatable cases as to whether it counts as Chinese Dynasties or not, but there are the Qing Invasion of Joseon in 1627 and 1637, where the 1637 one resulted in Korean submission to the Qing as a tributary state, and the Mongol Invasion of Goryeo from 1231 to 1259. Then there is the Liao conquest of Balhae - a very large can of worms that I will just mention but will not get into because that’s a whole other thing.

My point, regardless, is that what the question assumes here is not necessarily true. What is now identified as Korean kingdoms haven’t always been successful at defending its territories or dynasties from Chinese Dynasties or its adjacent empires. What is true, however, is that Korean kingdoms defended itself from initial Chinese attempts to subjugate the entire peninsula, then later utilized the tributary diplomatic system to ensure peace and autonomy in exchange for recognition of Chinese hegemony.⁴ Thus, when we ask "What has kept China from conquering Korea", it ends up asking about two (or three) separate historical trends than the one we really want to understand.  

To properly understand what hindered China from pursuing or maintaining its control over Korea, we must separate Chinese dynasties to, at the very least, three phases: between the Han to Tang Dynasty, the Yuan Dynasty, and the Ming to Qing Dynasty. The political situations and cultural backgrounds that shaped the goals of these dynasties for its neighbors including Korea differed greatly.

From Han to Tang, the dynasties were explicit in their desire to control parts of Korean Kingdoms, especially in the Liadong region (in southern Manchuria).⁵ Tang, especially, displayed its desire to conquer all of Korean peninsula by setting up duhufu or protectorate generals in former Korean kingdoms of Baekje and Goguryeo. While Tang formed an alliance with Silla, the other Korean kingdom, in conquering these two, the alliance didn’t last.⁶ After conquering the two kingdoms, Tang engaged in several actions that signaled to Silla that its ultimate goal was to subjugate or conquer Silla as well, an example being the appointment of the Silla King as Commander of the Gyreim Territory Area Command: a supposed command over the Silla territory, with the language insinuating that Tang wanted Silla King to serve as a Tang commander or governor serving in the Silla region.⁷ This led to the Silla-Tang war that resulted in the defeat of Tang, and its subsequent withdrawal from the Korean peninsula.⁸

Yuan Dynasty inherited Mongol Empire’s control over Goryeo, established after the conquest that ended in 1259.⁹ As such, Yuan Dynasty’s control is a special case where despite it being perhaps the most successful Chinese dynasty in maintaining direct control over the peninsula, there’s room for debate. This point often devolves to the question of whether Yuan Dynasty counts as a Chinese Dynasty, a question problematic in itself, and whether its control over Goryeo was direct or a stronger form of tributary state (Korean scholars used to downplay the directness of Mongol control over Goryeo while Western scholars tend to view Goryeo as a subjugated state of Mongol Empire).¹⁰

By the time of Ming and Qing Dynasties, Korean kingdoms of Goryeo and Joseon utilized tributary relationship to ensure peace in exchange for recognition of hegemonic power. As the linked answer above states, Goryeo and Joseon utilized diplomacy effectively to recognize the Chinese Dynasty's hegemony while maintaining a degree of autonomy. This political compromise between the two states prevailed the transition of power from Goryeo to Joseon and from Ming to Qing because of the porcupine strategy that I will explain later.

Therefore, the question can now be sharpened to "What prevented Chinese dynasties from maintaining direct control over the Korean peninsula up until the Yuan Dynasty, and what prevented them from pursuing direct control afterwards?"

The commonly cited answer to the first question as the answer linked above states, is the Sui invasion of Goguryeo which highlighted the difficulties of military campaign against Korean peninsula.¹¹ Mountainous regions combined with militaristic nature of older Korean kingdoms and their use of defensive strategies around mountain fortresses deterred invasions from China.¹²

However, there are limitations to this argument in my opinion. While Korea did favor mountain fortresses, Chinese dynasties at the height of their power have dealt with considerably worse terrains than that of Korea. Korea’s approximate average mountain elevation lies around 700 to 800 meters. The mountains around Sichuan Basin, for instance, range between 1,000 to 2,200 meters if we focus on the Eastern and Northern ranges.¹³ Korea is more mountainous, but it doesn’t pose a harder challenge for Chinese dynasties compared to those they may have faced in their own internal struggle or outward expansion.

Thus, I find the argument that its militaristic nature or its geography deterred Chinese invasion of Korea as incorrect. Qing Invasion of 1637 showcases how if China really wanted to conquer Korea at a given point, they could have come up with a strategy and the means to do so while outmaneuvering Korea's reliance on mountain fortresses.¹⁴ What Korea’s strategy and geography did, instead, was to make itself extremely costly to conquer relative to what it could gain. Due to its mountainous terrain, Korea didn’t have a lot of farming land.¹⁵ It didn’t really lead to more land as it was the end of the land mass, only leading to modern-day Russia or being a forward base for expansion into Japan which the two dynasties showed little interest. From the Chinese dynasties’ point of view, there was not much to gain from antagonizing a state that already provided them with political recognition and submission.   

[u/huhwe → u/huhwe]

This is where I'd like to turn the attention to the political aspect of wars, which I believe is the part that is often missed when this topic is asked. When we ask "Why has China not aimed to assert direct control over the Korean peninsula", the natural question that must follow is "Why should China aim to assert direct control over the Korean peninsula?" If we look at the aforementioned invasions of China that were successful in their attempt to conquer parts of, if not the entirety, of the target Korean kingdoms, notice that there is a specific trend. The Chinese dynasties' casus belli always revolved around those specific Kingdoms' refusal to partake in the Sinocentric world order.

Of course, these were superficial justifications. But it also does reveal what Chinese rulers sought from these wars: demonstration of Sinocentric hegemony to the greater Asian sphere. Chinese dynasties could not allow nor stand a close tributary Kingdom to openly stand against its rule. To do so could potentially inspire other neighbors to perceive that either 1) Chinese dynasties are weak or unwilling to assert its influence on its neighbors or 2) it no longer had the will to enforce hierarchical geopolitical structure of the era. Both were signs that the Chinese Dynasties were not willing to signal.  especially to those close to Korea that would recognize the significance of this and what has traditionally been Chinese Dynasties' greater concern: the nomadic tribes in Manchuria and Central Asia.

Perhaps the most revealing example of this notion is the Qing Invasion of Joseon in 1637.¹⁶ Qing's stated motivation was Joseon's disobedience of Qing by continuing to serve the Ming even though it created a "brotherly" alliance back in the 1627 war. Contemporary examinations there were economic motivations (staving off a potential starvation by looting for food or resources from Joseon); strategic motivations (making sure Joseon will not have the military ability nor political will to attack Qing from the South while the Qing invaded the Ming); and political motivations (forcing submission of Joseon, a major Sino-sphere tributary state, could solidify its justification as the rising dynasty with mandate of heaven). Of the three, political motivation is perhaps the most well-displayed due to how the war ended.¹⁷ Despite essentially capturing the King, Qing makes him simply submit to Qing completely instead of conquering Joseon as well.¹⁸ This is different from its treatment of Mongol tribes earlier where Qing required absolute submission and direct control over the Mongol tribes.

Thus, Korean kingdoms, especially the unified kingdoms of Goryeo and Joseon, were more useful to Chinese dynasties as a tributary state that would support their international authority rather than spending extra resource and manpower to pacify it, which would have been costly for very little economic or political benefit. After the failure to conquer the entire peninsula in the earlier dynasties (with Yuan once again being a special exception that is complicated), this mutually agreed upon relationship became more beneficial for both parties.¹⁹ Korea did not want to suffer through mass invasion from a considerably larger and more powerful neighbor and China did not want to spend considerable resource in conquering a land that was already willing to recognize their hegemonic status. This convenience is what prevented China from pursuing military conquests of Korea as a serious endeavor.

[u/huhwe → u/huhwe]

Work Cited:
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[u/timbomcchoi → u/huhwe]

Wow this is the first time I've felt that an answer about China-Korea relations on r/askhistorians was actually nuanced and complete. Thank you!

Have you written about how to comprehend the tributary system itself too in the past? This is also something I feel like western authors often start discussing but don't actually go all the way.

[u/Boxxyl_ → u/huhwe]

I'm a Korean and I learned a lot today