What was the main reason for Japan's isolation from China and Korea?

The main reason for Japan's intentional period of isolation, particularly from China and Korea—as well as from the West—was mostly driven by the desire to preserve its culture from foreign influence, maintain its sovereignty, and control external influences. During the Edo period (1603-1868), under the Tokugawa shogunate, this policy of isolation was known as Sakoku (鎖国), which translates to "chained country" or "closed country".

The Tokugawa shogunate enacted strict regulations on trade and prohibited almost all contact with foreign countries. Christianity, which was seen as a threat to the stability of the shogunate and to traditional Japanese values and norms, was banned, and the Christians in Japan were persecuted. The fear was that the spread of Christianity and the influence of powerful European nations would destabilize and divide Japan, and possibly lead to colonial domination as it had done in other parts of Asia and the Americas.

Japan's geographical location, being an archipelago separated from the Asian mainland by the Sea of Japan (East Sea), also played a part in facilitating this period of isolation. It was easier to control the borders and limit the influence from neighboring countries like China and Korea.

The policy was not absolute; some limited trade was allowed with select foreign countries, like the Dutch, who were confined to Dejima, a small artificial island in Nagasaki, and with the Chinese through a few designated ports. However, the isolation policy effectively cut off Japan from much of the world until the arrival of U.S. Commodore Matthew Perry in 1853, who pressured Japan into opening its borders, leading to the end of the Sakoku period.

Japan's isolation from China and Korea during the period known as the Sakoku ("closed country") era, which lasted from the early 17th century to the mid-19th century, was primarily motivated by a desire for political stability and the fear of foreign influence. Several key factors contributed to Japan's decision to close itself off from the outside world:

1. Fear of Foreign Influence: Japan witnessed the effects of European colonialism in neighboring Asian countries and was concerned about the potential for foreign powers to exploit and interfere with its internal affairs. The ruling Tokugawa shogunate aimed to prevent foreign influence and maintain control over the country.

2. Desire for Internal Stability: The Tokugawa shogunate, which came to power in the early 17th century, sought to establish a stable and centralized government after a period of civil unrest. They implemented a policy of strict control over the daimyo (feudal lords) and aimed to reduce internal conflicts. Isolating Japan from the outside world was seen as a way to avoid external disruptions to this stability.

3. Christian Missionary Activities: The arrival of European missionaries, particularly Jesuit and Franciscan missionaries in the late 16th century, led to the spread of Christianity in Japan. However, the Tokugawa shogunate grew concerned about the political implications of this foreign religion and the potential for it to serve as a tool for foreign powers. As a result, Christianity was suppressed, and missionaries were expelled.

4. Trade Restrictions: The Tokugawa shogunate implemented strict controls on foreign trade to limit external influence. Foreigners were restricted to the port of Nagasaki, and only the Dutch and Chinese were allowed to trade with Japan under tightly regulated conditions. This limited foreign interaction and prevented the spread of foreign ideas and technologies.

The policy of sakoku was only fully reversed in the mid-19th century when Japan underwent a period of rapid modernization and opened up to international trade and diplomatic relations during the Meiji Restoration.