How did a sailor's cloth from Genoa and Nîmes become blue jeans?

Through a long chain of cheap work cloth, a patent and then a movie star. The word 'jeans' comes from Gênes, the French name for Genoa, where a fustian textile of medium quality and reasonable cost was used for work clothes in general. The Genoese navy equipped its sailors with jeans, a fabric that could be worn wet or dry. In Nîmes, France, weavers tried to reproduce jean fabric but instead developed a similar twill that became known as denim, 'de Nîmes'.

The blue comes from indigo. In the most common type of denim only the warp threads are dyed, which is why jeans are predominantly white on the inside. Nearly all indigo came from plantations in India until synthetic indigo was developed in Germany in 1878.

The riveted trousers came in 1872, when a tailor named Jacob Davis wrote to the wholesaler Levi Strauss asking to partner on patenting clothing reinforced with copper rivets. They received a patent on 20 May 1873. The rivets reinforced points of stress, such as pocket corners and the base of the button fly. Early on these were simply sturdy trousers worn by factory workers, miners, farmers and cattlemen in the American West.

Fashion came later. After James Dean wore jeans in Rebel Without a Cause, they became a symbol of youth rebellion during the 1950s, and by the 1970s they had become general casual fashion in the United States.