Not too many years ago, it was common for clouds of smoke to hang overhead in America's restaurants, bowling alleys, college classrooms and even airplanes. That's because for much of the 20th century, smoking was considered rather cool. The trend toward widespread cigarette consumption began in the early part of the 1900s, when smoking became socially acceptable for women and cigarettes became easily accessible due to mass production and improved transportation [source: CDC].
In the 1940s and 1950s, studies on the link between smoking and various health problems were conducted, and it quickly became clear that smoking was related to major health concerns such as cancer and heart disease. The government created massive anti-smoking campaigns over the ensuing decades, and puffing away slowly lost its cachet. (It also helped that the government jacked up tobacco taxes and banned cigarette ads on TV.)
Eventually, when secondhand smoke was shown to be harmful, too, the federal government banned smoking in a wide variety of enclosed spaces, like offices, schools and even bars. All this legislation had an effect: Smoking among American adults has dropped from a high of 45 percent in 1954 to 15.1 percent in 2015 [source: NPR, Saad].
Smoking is still popular in other countries, though. And there's no way of knowing whether this longstanding decline in American cigarette consumption will continue. But back in the smoke-filled days of the mid-20th century, no one would have believed America's air would be so pure today.