In layman's terms: Its a fabric meant for work; the history dates back to the 16th or 17th Century as first used by sailors from Genoa Italy ("geans" get it?), but it was a mixed fiber fabric with silk as a component. Later it was produced in England and people believe that the French connection "serg de nime" was used as a marketing ploy by the English to give the fabric more clout.

It's when Denim finally hit American shores, with the massive cotton industry, that it became the 100% cotton product that we know it for today. It was used by ore and gold miners and anyone who's life consisted of hard labor. 

Trends in fashion are of course, not a new thing - Denim was first referred to as overalls because it was meant to go over clothes, not worn rocker fashion tight as is the case today. Eventually form over function prevailed and suspender buttons were replaced by belt loops, the old school clinch back was also abandoned, and as fashionable young Americans looked to distinguish themselves from previous generations- Denim was adopted by young Americans, then glamourized by Hollywood and exported back out to the world.

One of the most interesting facts about the origin of Denim is that in WW2, the American GI' s actually introduced the Japanese to this American created garment and today you can't mention denim without a discussion on the Japanese looms which create the world's best Selvidge- the japanese took a perfect fabric and perfected further. Why i love it?  Because I'm an American man; and I like tough things.

Its importance?  Its a fabric that carries the history of countless American and non-Americans. The uniform of the 19th and 20th century Explorers and Workmen. Its a fabric that fades with its wearer and holds up long enough to create a personal history through wear marks, in turn a color and shape palate ever differing and unique. Kinda like the USA!