Odd Arne Westad is a professor of history at Yale University and has a distinguished record of publication on East Asian history and politics and the Cold War. This new work is based on the Edwin O Reischauer Lectures that he gave at Harvard in 2017. Such lectures generally fall into two categories. They either present a piece of ground-breaking research in an accessible form or, as Westad does here, provide a valuable and wide-ranging assessment of a particular subject.

The China–Korea relationship has puzzled the West since at least the 18th century. While Korea seemed to be a separate political entity from China, those wishing to trade or have another form of involvement with the country soon came up against an obstacle. Koreans insisted that they could not do things without Chinese permission, while still maintaining that Korea was an independent country. Westerners, convinced that their system of fully independent states, developed after the 1648 Peace of Westphalia, was the norm, failed to see in the Chinese approach characteristics that had once prevailed in Europe. Westad hints at this but does not explore it in detail. He also hints at, but again does not examine, the long-standing special relationship between China and Korea in the 1,300 years before the Ming dynasty came to power in the former in 1368 and the Chosun dynasty in the latter in 1392. During that time, Chinese dynasties had been closely, if spasmodically, involved with Korea as the disparate kingdoms on the peninsula slowly coalesced into one unified entity. Sometimes, the relationship had been a peaceful one. From China came a writing system that has faded from use only in the last seventy years. Korean government, architecture, city layout and religion all had their origins in China. In time, of course, they were modified and changed to become something recognisably different, but even today Chinese links can be discerned in both Koreas.

Not all interactions were peaceful. The Yuan dynasty that ruled China from 1271 to 1368 and its predecessor, the Mongol empire of Kublai Khan, treated Korea very harshly and effectively imposed subjugation on the country. The Koreans welcomed the overthrow of the Yuan and its replacement by the Ming. But the experience of the Mongol period also led them to seek ways to accommodate their large neighbour. This approach was known as sadae (‘looking up to the great’). To prevent interference in the peninsula, the Korean monarchy formally deferred to the emperor in Beijing. The Koreans notified the Ming court of important developments, such as the death of a monarch and the accession of his successor. The Chinese did not become involved in the succession itself but imperial approval conferred legitimacy. Korean congratulatory missions visited Beijing on auspicious occasions, while the Koreans also looked to China for assistance when threatened by outside forces, such as the Japanese in the 1590s. The Chinese were not always keen to fulfil their side of the bargain, but, given that Korea might provide a route into China itself, which the Japanese certainly sought to exploit, on that occasion they eventually did send assistance.

It was two-way traffic. When the Ming empire came under Manchu attack in 1616, it sought and received Korean aid. Korean troops went to support the Chinese but ended up surrendering in the hope of saving their own country from attack. This worked in the short term, but as the Manchu prepared to attack the Ming again in the 1620s, they first invaded Korea. The north of the country was devastated and the king and the court were captured. The Manchu, whose leader, Hongtaiji, began styling his family as the Qing dynasty in 1636, established themselves as rulers of China in 1644, whereupon the Koreans shifted their support from the Ming to the Qing.

The Koreans may have looked down on the Qing as parvenus, but the traditional pattern of relations continued until the Qing defeat by the British in the 1840s. Koreans still sought Chinese advice on the handling of foreign affairs, yet were also aware of the problems facing China. From the 1860s, Western pressure grew on Korea to ‘open up’, as China and Japan had done. By the 1870s, the Japanese too had their eyes on Korea. As usual, the Koreans turned to China for support. But China was unable to help them, instead encouraging the Koreans to conclude treaties with Japan and Western powers in the face of growing pressure. China and Korea continued to claim that Korea was both a dependency of China and independent. Foreign powers sometimes followed one tack, sometimes the other.

Japan settled the issue. When Korea asked for Chinese help in 1894 to cope with a major rebellion, China responded, effectively breaking an earlier agreement with Japan to consult with Tokyo before taking action of this sort. This led to the 1894–5 Sino-Japanese War and China’s unexpected defeat. Under Japanese pressure, Korea declared its independence from China, but what it got in exchange was a new form of subservience to Japan. Only Russia challenged the Japanese hegemony, leading in 1904–5 to the Russo-Japanese War, which Japan won. Korea became a Japanese protectorate and then was annexed by the country in 1910. There followed thirty-five years of increasingly harsh colonial rule. Westad sees this in a more benevolent light than I would. There were improvements in areas such as communications and education, but they mostly benefited the Japanese. He also plays down the continued role of China in Korean affairs during this period. Political turmoil did not end China’s cultural pull, while Koreans of all political hues fled to China, which became a base from which to oppose Japan.

Developments after 1945, with the emergence of two Korean states on the peninsula, one communist, the other nominally democratic, and the eventual victory of the Communist Party in the Chinese Civil War, clearly changed the dynamic. The great powers once again involved themselves in Korean matters, not necessarily to the advantage of the Koreans. Westad, who has written a major study of the Cold War, sees the Korean War (1950–53) very much in the context of that struggle, playing down the civil nature of the conflict. What it did reveal, he makes clear, is China’s ongoing influence on the peninsula, which continues to this day. But as two thousand years of history have shown, China’s role in Korea is a complex one. Westad’s short and stimulating study provides many clues to understanding that relationship. It does not fully penetrate it, but it is good place to begin.