Sushi was originally invented in Southeast Asia in the 4th Century BC as a method of food preservation. The natural fermentation of rice preserved the fish, which after a few months could be eaten and the rice thrown away. This type of sushi is called nare-zushi.

Sushi was introduced to Japan around the 8th Century AD. The Japanese preferred to eat rice together with fish, calling it haya-zushi; this dish was unique to Japanese culture. At this point, sushi was no longer a means of preservation but rather a form of cuisine. Sushi was created using rice vinegar and even vegetables.

Nigiri-zushi originated at the start of the 19th Century, when Tokyo was still called Edo. Edomae, which literally means "in front of Tokyo bay," was where the fish and seaweed for the nigiri-zushi were obtained. After the Great Kanto earthquake in 1923, the chefs from Edo traveled throughout Japan for work and spread the consumption of nigiri-sushi.

Sushi has grown in popularity mostly due to raised health awareness. As a fresh and healthy alternative to fast foods, sushi bars have cropped up all of the United States.

(source: sushi-master.com)