I would say weather, obesity and technology also play major roles, possibly more than "fashion" or maybe creating fashion. Weather: During the 20th century Ame

I would say weather, obesity and technology also play major roles, possibly more than "fashion" or maybe creating fashion. Weather: During the 20th century Americans have increasingly moved west and south to warmer climates (go back 100 years and most Americans lived in the cooler climates in the north east). Loose khakis, t-shirt and sandals is much more comfortable in warm weather. Obesity: Very few were obese back when suits were common. It's not comfortable anymore to tuck your shirt in the pants once the belly pushes outwards (personal experience). Technology: Washers and dryers became common throughout the 20th century. Washing clothes used to be time consuming but the washer and dryer meant that it's now easy to wash your jeans and t-shirts. Meanwhile it's still a hassle to have your suit dry cleaned and your shirts pressed or ironed.