President Trump often mentions his wish that the Japanese government would pay more for the U.S. bases and troops in Japan. Similar demands are now being negotiated between the U.S. and South Korea.

But Japan has been annually paying about 4.5 billion dollars for this, taking upon herself no less than 75% of the costs of the stationing. That makes it even cheaper to keep the U.S. troops in Japan than in the U.S. So before embarking on official negotiations on who should pay more for what, let us sort out things first.

　Nevertheless we have to thank the U.S. for her efforts to maintain peace around Japan, and particularly for her remarkable assistance rendered after the large earthquake and tsunami in North-East Japan in 2011. That again demonstrated the depth and warmth of the bonds between the two countries.

Genesis

1) Things started from post-war occupation of Japan
If one country uses bases in a foreign country, the former usually pays for it to the latter. Isn't it strange that Japan pays to the U.S. for the use of bases in Japan (by the way similar burden-sharing exists between the U.S. and her European allies, too)?

The genesis of this is, of course, the Second World War, after which the U.S. troops occupied Japan until 1952, when Japan regained its sovereignty by virtue of the San Francisco Peace Treaty. This treaty was concluded just in the middle of the Korean War, therefore it encountered a strong resistance of the U.S. military, which wanted to keep Japan as an ideal bridgehead for the Korean Peninsula.

The Japanese government and the U.S. State Department persuaded the U.S. military by signing a security treaty (Treaty of Mutual Cooperation and Security between the United States and Japan), in which Japan offered several bases for American free use. It was not an "alliance" treaty per se, because Japan at that time was totally disarmed, and because the treaty did not formally obligate the U.S. to defend Japan. It effectively was a continuation of occupation.

2) Japan started to share burden in 1960
In 1960 the Security Treaty was amended, in which the obligation of the United States to defend Japan in case of emergency became unequivocal. At the same time a status of forces agreement (Japan-U.S. Status of Forces Agreement) was signed, stipulating that the Japanese side shall totally pay for the ground rents of the bases and for the social benefits of the Japanese laborers employed by the U.S. forces. These payments today amount to 1.65 billion dollars.

But many Americans were not aware of this financial burden sharing, and started considering the arrangement unfair, because the Japanese side is not obliged to help the American troops, even when the latter engages in battle to defend Japan. In NATO the obligation is mutual; the European allies should render help when the U.S. is attacked.
The arrangement with Japan was unilateral, because Japan prohibited herself from using armed forces (except for cases of self-defense) by virtue of the post-war constitution, which was initially imposed on Japan by the Americans, but later was fervently cherished by Japanese pacifist voices. In a sense the Japanese tied their own hands and therefore, could not seek a more equal status with the U.S. in security.

Meanwhile, the American voices about unfairness of the alliance became louder, after the Japanese economy saw a rapid growth, and even more so after the yen's value soared twice in the 1970s. Because of the fall of dollar's value by twice the life of American troops and their families in Japan became unbearable.

3) In 1978 Japan added new budget
Therefore, in 1978 the Japanese government started the so-called "sympathy budget" for the American troops. Namely, the Japanese started to pay for the most part of the labor costs for 23,178 Japanese employees in the bases, the utilities costs and the training relocation costs (the sum today is about 1.3 billion dollars annually), exceeding her legal obligation as stipulated in the U.S. - Japan Status of Forces Agreement.

Today the U.S. can keep her armed forces in Japan cheaper than in the U.S.

Today Japan pays 1.65 billion dollars on the basis of the Status of Forces Agreement, and 1.3 billion dollars by "sympathy budget". The total sum (including other items) is about 4.5 billion dollars, meaning that Japan pays no less than 75% of the costs of U.S. troops stationing.

These arrangements provide very favorable conditions for stationing of the American troops in Japan; indeed, for the U.S. government it is cheaper to keep them in Japan than in the U.S.

But Japan failed to convey this information to the Americans, so the condemnation of the "unfair" nature of the alliance never ceased in the U.S. This is the product of the old perception, which had been formed before Japan started to pay lavishly as explicated above. In fact, if Japan pays more, the American troops will be degraded into a position of being mercenaries.

Japan is increasingly helping the defense of the U.S.

Things have changed not only in Japan's financial burden sharing as shown above, but also in Japan's readiness to fight jointly with the U.S. in case of emergency. In 2014 Japan adopted new legislation to empower the Japanese Self Defense Forces to operate to defend the U.S. in the cases which would directly affect Japan's own security.

Before this new legislation it was not legal to deploy Japan's Self Defense Forces even for the American troops which are battling to defend Japan. This absurdity arose, as I mentioned above, because the Japanese people preferred to stick to the post-war constitution which denounced all kinds of uses of armed forces. Now the Japanese government amended the interpretation of the constitution, freeing itself from the long self-imposed shackles.

On top of that one should note the fact that even before this new legislation Japanese Self-Defense Forces with Aegis warships, P-3C anti-submarine patrol planes and robust submarine fleet had been coordinating their operation with the American forces and engaging in joint exercises to guard the U.S. aircraft carriers et.al. A substantial part of Japan's Self Defense Forces would have been assigned for effective joint operation in case of emergency.

Building up Japan's own (conventional) forces

Japan's defense budget is now the eighth largest in the world. The Maritime Self-Defense Forces possess about 50 major battle ships (including two helicopter carriers which are being converted to full-fledged aircraft carriers), 19 submarines et al. Japan recently strengthened her coast guard in order to defend the Senkaku Islands (China claims the ownership). It is striking that Japan is now boldly acquiring weapons, which can attack adversary's bases overseas. In the past opposition parties under the influence of the Soviet Union and China used to vehemently oppose any acquisition of such weapons.

Today the opposition parties condone the introduction of long-distance weapons as long as they do not incur danger to the lives of the Japanese. Therefore, Japan is now building long distance transport airplanes, aircraft carriers as stated above, and is poised to purchase from Norway airborne intermediate-distance cruising missiles (without nuclear warheads). Thus, Japan today is not totally dependent on the U.S. for her own defense, though Japan still needs the American forces as deterrence (nuclear deterrence inter alia).

Bases in Japan are the fulcra for deployment of U.S. forces to the Middle East et al.

In calculating the appropriate sum of Japan's financial burden sharing it is important to note one thing: the fact that the U.S. troops use the Japanese bases not only for defense of Japan but also for defense of South Korea and for deployment of the forces in the West Pacific, the Indian Ocean and even in the Middle East. The Fifth Fleet of the U.S. Navy based in Bahrain does not possess its own vessels. The fleet depends on the Pacific Fleet for warships, and in case of war use of Yokosuka navy base in Japan becomes vital; without Yokosuka U.S. Navy vessels will have to go back as far as to California for major checks and repairs. Then is it not the U.S, South Korea and others who should pay for the use of the Japanese bases?

But the U.S. would retort, saying that maintenance of peace in the Middle East and maintenance of safety of the sea-lanes would serve Japan's interest, too, therefore it is Japan who should pay for the service. This argument is partly right, but when the U.S. policy engenders unsolicited conflicts like in the case of the Vietnamese War and the Iraq War, Japan cannot find convincing reasons to pay for them.

As regards the safety of the sea-lanes, there is no need to worry about their safety until the very day when a real war occurs between the U.S. and China, because maritime safety is needed for China as well and she would not dare to disrupt it in peace time.
All in all Mr. Trump's argument is not logical enough, and his demands can be boiled down to more blunt words, "Japan, you have money. Give me that."

Nuclear deterrence is the stumbling block

However, there is one thing in which Japan is totally dependent upon the U.S.: nuclear deterrence. In the past the "allergy" against anything nuclear was so strong in Japan's society that it was a taboo to talk about this, but things are gradually changing.

The Japanese society, which had not been roused by the large arsenal of the Chinese nuclear missiles, suddenly became worried about North Korean missiles. These missiles look "real" as compared to the Chinese ones, because they have already flown across Japan's territories and because President Trump may condone them. For President Trump only the long-distance missiles, which can reach the U.S., matter, and the shorter-range missiles are "a matter for Shinzo Abe" .

Therefore, Japanese pundits started to raise the issue more and more boldly, discussing a whole range of possibilities, from strengthening of the American "nuclear umbrella" to possessing Japan's own nuclear weapons.

However, "Japanese own nuclear weapon" is a thing for the future. First of all no town in Japan would allow one to be located in their own backyard. Secondly, the U.S. would not allow Japan to possess her own nuclear weapon for various known reasons.

Secretary of Defense Mark Esper once suggested an intention to station newly-developed intermediate-range nuclear missiles in allied countries, including Japan, but except for stationing them in some remote un-inhabited islands this would be a pipe dream.
Therefore, the most realistic solution would be strengthening of the U.S. nuclear deterrence in the West Pacific. Namely, intermediate-range cruising missiles with nuclear warhead should again be mounted on the U.S. submarines and on the bomber planes. If Japan allows occasional visits by such submarines and bombers based in Guam Island, it will serve as a deterrence force for Japan.

Japan also needs quid pro quo for her money

If Japan ever pays more for the stationing of the American troops in Japan, she may well demand a quid pro quo. Firstly, we need a better nuclear deterrence as discussed above. And secondly, Japan needs more information to be disclosed when she imports advanced weapons from the U.S. The thing is that the U.S. "Foreign Military Sales (FMS) Program" impedes disclosure of technological information to foreign buyers.

There are several understandable reasons for this esotericism, but when a newly purchased fighter plane F-35A crashed off-shore Japan in April 2019, the Japanese lacked in technological information to identify the cause of failure and to take preventive measures. It makes future use of American weapons very risky and let the Japanese become more inclined to purchase weapons from the third countries.

Recovery of Japanese sovereignty (liquidation of the remnants of the post-war occupation)

As Japan takes upon herself a heavier burden, the remnants of the post-war occupation, that is the limitation of Japan's sovereignty in her own territories, should be corrected. Firstly, air traffic control over the vast area around Tokyo should be returned to Japan (currently civil aircrafts are not allowed to use this area without permission of the U.S. forces stationed near Tokyo). In Germany, for example, air traffic control is the prerogative of the German authority. Secondly, the Japanese police and other authorities should be allowed to enter the American bases, which is the case in Germany and Italy.

President Trump's exhortation to Japan to pay more for the American troops in Japan offers a good opportunity for a stock-taking of the alliance between Japan and the United States in order to align things on a more rational and fairer basis.