The Japan-U.S. alliance originated in bilateral cooperation during the Korean War.
Since the Meiji era, the Korean Peninsula has been central to Japan’s security, and in the postwar period Japan’s defense structure has been built on a division of roles within the alliance with the United States.

The origins of the Japan-U.S. alliance lie precisely in Japan-U.S. cooperation during the Korean War.
2018-01-10
The following is from an article by Professor Kazuya Sakamoto of Osaka University published in this month’s issue of the monthly magazine WiLL.
Had it not been for the trials that God gave me, I would likely have remained at Kyoto University as my high school mentor sternly instructed and lived my life as a scholar.
Professor Sakamoto graduated from the Faculty of Law of Kyoto University and now serves as a professor at Osaka University, the alma mater of my friend.
Upon reading this article, I felt that this was not merely a coincidence.
Regarding the passages surrounding his statement “It is said that China seeks hegemony. However…,” readers will likely think that the correctness of the “hegemonic stability theory,” which marked the beginning of my Turntable of Civilization, is being proven by Professor Sakamoto.
Emphasis in the text except for the headings is mine.
Does a China seeking hegemony have any friends.
Leaders who are not elected must constantly demonstrate the legitimacy of their rule through achievements.
The cornerstone of security is the Korean Peninsula.
The year 2018 marks the 150th anniversary of the Meiji era.
As this is a fitting milestone, why not take this opportunity to recall the history since the Meiji Restoration and reconsider Japan’s diplomacy and security.
Japan now faces the threat of North Korea’s nuclear and missile development, but for the past 150 years the Korean Peninsula has been a key location for Japan’s security.
From the Meiji era until before the war, self-defense for Japan included the security of the Korean Peninsula.
The Sino-Japanese and Russo-Japanese wars were fought to prevent large hostile powers from advancing into the Korean Peninsula.
The Korean Peninsula is shaped like a dagger protruding from the Asian continent toward Japan.
Japan had to protect the peninsula for its own defense, even by dispatching troops.
After the war, however, this changed.
Postwar Japan, having grown weary of overseas deployments, became a country that would not, could not, and did not wish to send troops to the Korean Peninsula even for self-defense.
That is acceptable, but it does not mean that the Korean Peninsula ceased to be related to Japan’s self-defense after the war.
So how should Japan ensure its self-defense, including the security of the Korean Peninsula.
This came to be managed through cooperation with the United States, namely the Japan-U.S. alliance.
The origins of the Japan-U.S. alliance lie precisely in Japan-U.S. cooperation during the Korean War.
In that war, Japan left the security of the Korean Peninsula to the actions of the U.N. forces centered on the United States and devoted itself to supporting them by providing bases and other assistance.
In the year following the armistice of the Korean War (1954), when the Self-Defense Forces were created, the Diet passed a resolution prohibiting overseas deployment, and it is clear that the “overseas” referred to here had the Korean Peninsula in mind.
It was decided that even if something were to occur again on the Korean Peninsula, the Self-Defense Forces would not be dispatched.
Sixty years later, in 2014, the government changed its constitutional interpretation regarding the right of collective self-defense, yet even then Prime Minister Shinzo Abe clearly stated in the Diet that Japan would not exercise collective self-defense on the Korean Peninsula to assist U.S. forces.
The Self-Defense Forces will not be dispatched to the Korean Peninsula; instead, if necessary U.S. forces will be deployed, and Japan will support them.
This division of roles within the Japan-U.S. alliance enables Japan, unlike in the prewar era, to fulfill its self-defense without directly going to the Korean Peninsula itself.
In recent years this framework has been significantly strengthened through new security legislation and guidelines, but Japan now faces a severe test as to whether it can respond effectively to the current North Korea issue.
To be continued.