In the upcoming summit between the U.S. and North Korea, what if the Workers’ Party of Korea Chairman Kim Jong Un demands the withdrawal of U.S. Forces Korea (USFK) and President Donald Trump accedes to the demand?

Even though North Korea might agree to abandon its nuclear weapons and ballistic missiles in some fashion, the withdrawal of USFK would directly impact Japan’s security, so Japan should not remain on the sidelines.

In the scheduled meeting with President Trump this month, Prime Minister Shinzo Abe should once again align his understanding about the significance of USFK with that of the president. As well, now is the time for Japanese politicians to discuss this matter of life and death for Japan. 

A U.S.-South Korea joint military drill in preparation for a contingency on the Korean Peninsula began in South Korea and its surrounding waters and airspace. About 24,000 American troops mostly from USFK and about 300,000 South Korean troops will conduct field training and tabletop exercises until early May. This is an important opportunity to put effective pressure on North Korea.

In order to deter North Korea from invading South Korea, USFK mainly comprises army troops, without which the U.S. would not be able to protect the ROK. For that reason North Korea persistently demands the withdrawal of USFK from South Korea.

The withdrawal of USFK would significantly impact Japan.

In a diplomatic sense, the U.S.-South Korea alliance would be dissolved or become a mere formality with no military foundation and there would be a risk of the ROK shifting from a pro-U.S. and pro-U.S.-Japan alliance stance to a pro-China stance. 

In a military sense, Japan would have to enlarge its area of defense to include, in addition to the Nansei Shoto [Southwest Islands], areas near the Korean Peninsula. Specifically, Tsushima would be at the forefront of Japan’s defense.

From the medium- to long-term perspective, there is a possibility that the Chinese navy and air force would use the mainland of South Korea and Jeju Island in the absence of a U.S. military presence.

Although Japan and South Korea cooperate with each other to some extent including sharing information on North Korea’s ballistic missile launches, it would become uncertain how long this cooperation would continue after the withdrawal of USFK from the ROK.

The withdrawal of USFK would lead to the dissolution of the UN forces in South Korea. U.S.  bases in Japan are designated bases for use by UN forces in the event of a contingency on the Korean Peninsula. If they would  no longer fill that function, the blue UN flag would be lowered. This means that Japan’s deterrent capability based on the presence of UN forces bases in the country would be lost.

The role of the Self-Defense Forces would expand. The current defense equipment and budget would become insufficient to defend the country.

The withdrawal of USFK alone would change Japan’s basic security structure, which the country has relied since the Korean War Armistice Agreement was signed in 1953, and also require Tokyo to transform its defense posture. Sharing such an understanding with President Trump is an urgent task.