By Deirdre Clemente

I study one of the most profound cultural changes of the 20th century: the rise of casual dress — the “why” and “when” our sartorial standards went from collared to comfortable.

As Americans, our casual style uniformly stresses comfort and practicality. A hundred years ago, the closest thing to casual was sportswear — knitted golf dresses, tweed blazers, and oxford shoes. But as the century progressed, casual came to encompass everything from worker’s garb (jeans and lumberman jackets) to army uniforms (khakis). Americans’ quest for a low-key style has stomped on entire industries: millinery, hosiery, eveningwear, fur. It has infiltrated every space from the boardroom to the classroom to the courtroom.

Americans dress casual. Why? Because clothes are freedom — to choose how we present ourselves and to blur the lines between man and woman, old and young, rich and poor. The rise of casual style undermined millennia-old rules that dictated noticeable luxury for the rich and functioning work clothes for the poor. Until a little more than a century ago, there were few ways to disguise your social class. You wore it — literally — on your sleeve. Today, CEOs wear sandals to work.

Despite the diversity of choice in the clothing market today, so many of us tend toward that vast, beige zone between Jamie Foxx and the girl who wears pajama bottoms on the plane. Casual clothes are the uniform of the American middle class. T-shirts, jeans, and wrinkle-free shirts make “middle classness” available to anyone who choses to put it on. And in America, nearly everyone wants to put it on because nearly everyone considers himself or herself to be middle class.

Our country’s casual style is America’s calling card around the world — where people then make it their own. It is witnessed by the young boy on the Ivory Coast wearing a Steelers jersey and in the price of Levi’s on the black market in Russia. Casual is diverse and ever changing, but it was made in America.

The introduction of sportswear into the American wardrobe in the late 1910s and early 1920s redefined when and where certain clothes could be worn. The mass acceptance of sportswear coincided with the consolidation of the American fashion industry. By the end of the 1920s, firms produced designs, worked with manufacturers, and marketed specific kinds of garments to specific demographics.

A second milestone was the introduction of shorts into the American wardrobe. The popularity of bicycling in the late 1920s brought about a need for culottes and shorts. Shorts remained time-and-place specific for women (gardening, exercising, and hiking), until the Bermuda shorts craze of the late 1940s, when women turned plaid wool shorts into legit fashion.

At all-male Dartmouth College in May 1930, the editors of the student paper challenged their readers to “bring forth your treasured possession — be it tailored to fit or old flannels delegged” so that the men could “lounge forth to the supreme pleasure of complete leg freedom.” The Shorts Protest of 1930 brought out more than 600 students in old basketball uniforms, tweed walking shorts, and newly minted cutoffs, and introduced shorts into the American man’s wardrobe.

Americans moved into the 1950s with more options to self-create than ever before. Fundamental to this freedom is a “unisexing” of our wardrobe, a third milestone on our quest to go casual. Women didn’t really didn’t wear pants until the 1930s, and it was not until the early 1950s that pants made it mainstream. There were still discussions and regulations about women in pants well into the 1960s.

That decade saw seismic shifts in “unisexing.” Women adopted T-shirts, jeans, cardigans, button-down collared shirts, and for the first time in nearly 200 years, it was fashionable for men to have long hair.

To dress casual is quintessentially to dress as an American and to live, or to dream of living, fast and loose and carefree.

Deirdre Clemente is a scholar, public historian, and teacher. She is the author of “Dress Casual: How College Kids Redefined American Style” and served as a historical consultant for the Baz Luhrman film, “The Great Gatsby”. She wrote this for What It Means to Be American a national conversation hosted by the Smithsonian and Zocalo Public Square.