Sushi originated in China around the 2nd century when fish was preserved by storing it in rice to ferment. This practice spread to Japan where the rice was eventually eaten alongside the fish. In the 17th century, rice vinegar was added to the rice, allowing sushi to be eaten immediately. Then in the 19th century, sushi was transformed by placing the fish atop rice instead of inside, creating a fast food. After World War II, sushi spread globally and is now popular worldwide.