When the Allied forces arrived in Japan in 1945 for what was to be the seven year military occupation, there was little doubt that the country would be changed forever. However, some traditions were retained in an effort to maintain Japanese culture. One of these traditions was sushi.
The earliest form of sushi in Japan was called narezushi (salted fish). Fish was stored in fermented rice for long periods of time without spoiling and provided an important source of protein in the Japanese diet. The sushi we are familiar with today is called nigiri sushi. It had its origins in Edo (Tokyo). A restaurant owner named Hanaya Yohei is credited with having invented this type of sushi during the 19th century. The Edo people were known for their busy lifestyle and lack of patience, therefore many fast food businesses began cropping up. Nigiri sushi, which was known as Edomaezushi at the time, was a type of fast food, conveniently shaped to be eaten by hand and no longer reliant on the fermentation process utilized by narezushi.
While nigiri quickly became the most popular style of sushi in Edo, it did not immediately dominate the sushi landscape as it does today. There were two events which aided the popularity of nigiri sushi outside of Tokyo: one was the Great Kanto Earthquake of 1923 and the other was the military occupation of Japan in 1945. The earthquake caused many people to leave Tokyo and return to their hometowns. Among these were the various sushi chefs who opened restaurants upon returning home and served Edomaezushi to their clientele. In post-war Japan, many sushi shops were forced to close due to the rice rationing at the time and not allowed to reopen.
Eventually it was impressed upon the American Forces General Headquarters that the sushi restaurants should be allowed to reopen as sushi was an important part of Japanese culture. When the restaurants reopened however, they had to adhere to one strict rule. That rule was that the patrons were to bring in their own rice rations for the sushi. One cup of rice was to be used to make ten pieces of sushi hence the nigiri sushi shrunk in size. In pre-war Japan, nigiri sushi was three times larger.
Eventually the same system was implemented throughout Japan and Tokyo style nigiri became Japan’s predominant form of sushi.